With the subframe and suspension in place so the car could sit on four wheels it was time to start fitting sheet metal. Trunk lid was first up and with some tweaking the new (used) lid lines up nicely. So I moved on to the front end where my first task was to figure out if the 81 subframe would work with the 70 core support.

The later frame mounting holes for the core support are farther apart than on the early frame and the directions for the PTFB solid body mounts say they can't be used with the 70-73 Firebird core supports. BUT, I paid for the solid mounts and I'm using them! I marked and opened up the body mount holes in the subframe to fit the sleeves that come with the PTFB solid mounts. While opening up the holes for the solid mounts I found that the bushings wouldn't sit flat inside the frame rail because of the way the frame is made (like the rear most body mounts) so I welded in some sheet metal pieces I made.

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Next used my tram gauge to measure and mark the core support for the new body mount location and larger diameter. Then opened up the holes in the core support for the mounts. I made the holes slightly bigger than necessary to allow a bit of side to side and fore/aft adjustment of the core support.

I had poly body mounts previously I installed back in the 90's. At the time I used a 1/2" thickness bushing between the frame and core support as instructed. I always had a lot of shim stacks to get good fender/bumper/hood gaps and so I'm test fitting the body panels with the thick 1" bushing between the frame and core support to see if things fit well with them (if not I'll switch to the 1/2" and test fit again). If the 1" bushing doesn't work out I'll come back and modify this post.

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]After deciding the solid mounts can and will be used for the core support I enlisted my buddy Jeff to give me a hand installing the fenders etc. and starting to line things up so I can do blocking on the doors, hood, and fenders before the final coat of primer.

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With the sheet metal roughly in place and waiting on some new bolts for the bumper I mounted the tall rear spoiler I'd roughed in a while back so I could sand it in place on the car and get the pieces uniform and contoured nicely.

In the top pic pic (before being installed for sanding) you can see where the fiberglass was added and about how much taller this spoiler will be compared with the original. The idea being to make it fatter than it needs to be, then sand till it looks right to me, then a skim coat of filler and block sand till straight/smooth, then prime/block/prime. I'll also be mounting up my old rear spoiler for the same procedure and will keep it the stock size so I have my choice of regular spoiler or spoiler on steroids for track use. Last pic shows a guide I made to get the spoiler height uniform and curved like the decklid, sticky sandpaper is used on the plywood part.

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In brief it's a 1961 Impala 2 door Sport Coupe (hard top / bubble top) with an LSx swap, big brakes, tubular suspension, lowered and 18" wheels, in the process of a rustoration / update. Lots of fabrication and lots of small one-off custom touches.

The plan is improved handling and ride that will be driven (and beaten on) cross country at any random point with new car reliability.



That is an excellent tip on the fasteners. One of the places to save money on a car is not in fasteners.

The spoiler is looking great. Very nice job getting the height you need and keeping a factory look for the uninitiated.

Your thread is giving me some really good ideas. Thanks again.

I'm curious to see how the spoiler turns out. That's something I've thought of doing in the future. Thanks for the updates John.

Sounds like a cool car and I'm sure others like myself would love to see it. If you don't want to make a project thread then at least add it to the garage built thread with the description you wrote above copied and pasted. I had a very low miles 64 Biscane back in the 90's, not as cool as a bubble top though and was the last of the Chevy X frames.

More on the spoiler!


The rear spoiler is a focal point on a lot of 2nd gen F bodies and very easy to see. Since they're 35-45 years old now most have deformed or been damaged over time. The plastic slowly drying out and shrinking causes them to become wavy and crack. Some are worse than others of course and I'm lucky the two I'm working with were in pretty good condition to start with.

The tall one I'm making was from a 76 and needed some stripped threads repaired and missing studs replaced so I welded some small washers on 1/4" X 20 threaded rod and made several replacement studs (since I couldn't buy any locally). While I was making them I made the threaded part that screws into the spoiler a little bit longer to grab virgin threads at the bottom of the holes. Several drops of fiberglass resin in the holes before installing the new studs carefully and problem solved.

Next issue with spoilers is getting them to line up as well as we'd like. Often we're dealing with used or aftermarket quarters, deck lids, tail panels etc. which may not be the same as original. Our standards for panel alignment and gaps has raised quite a bit over the years since these cars were new and even when new the alignment/gaps weren't all that great from the factory. Here's my way of bringing old rear spoilers back to usable condition with better fitment and gaps than stock. I'm sure others have different ways of accomplishing the same goal and there's more than one right way to do things.

Strip the spoiler with 80 grit and clean old paint, sealers etc off the inside of the spoiler around the mounts and pads it sits on where it meets the body. Then install center section on trunk lid (trunk lid aligned previously). Clean old paint, sealers etc off the inside of the spoiler where it meets the body. If the mounts on the inside of the spoiler have to be modified by grinding a little off so the spoiler sits nice, so be it. Also, the holes in the decklid may need to be ovalized a bit to get the center section where you want it. Once happy with the center section, snug up the nuts on the ends to hold it in place. Then install end caps and see if you can get them lined up pretty well with the center section with the nuts snug. Again, may need to slot holes or modify the inside of the spoiler cap so it sits nice on the fender. Be patient, take your time and shuffle the pieces a little one way or another to get the pieces to sit as nice as possible on the sheetmetal and have the best gaps. If necessary move the center section a little and try again, when satisfied tighten the nuts. Then...

The ends of the caps and center section have often been sanded for previous repaints and the plastic has shrunk and deformed so after 35-45 years they're usually not very flat anyway. Apply a coat of your favorite body filler over the gaps between the end caps and the center section, don't try to fill the entire void, just bridge the gap. Ya, I know, it just seems wrong. Then use a hacksaw to cut a slot centered where you'd like the center of the finished body gap between the center section and end caps to be. Next use a thin file like a saw and cut the gap wider. Then use thicker and thicker files to widen the gap till it looks the way you want. Using the files keeps the slot straight and even because they don't flex much. If you want to move the gap a bit one way or another just apply pressure to the file as you're cutting with it. Once you've got the gap where you like it open the trunk and apply filler to the voids on the ends where the filler used to bridge the gap didn't go. Then close trunk and use the file again, repeat as needed till the ends just have little voids and pinholes in the bondo.

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Because the spoiler plastic has shrunk, warped etc. over the years They're not straight anymore. At a minimum they'll need high build primer and block sanding. I'd hoped that would be all I needed to do for the one below but as you can see after some blocking on the one in the pic below I've already cut through the primer to the plastic and haven't even removed the guide coat in the low areas where the mounts hold the spoiler to the car. This was on a spoiler that spent 99% of the last 25 years in a garage since I did the car the first time. I've seen the same pattern before and apparently the mounts pull enough so the spoilers deform as the plastic gets old. The cure is to skim coat the whole spoiler with filler (front and back) then block sand the filler with the spoiler attached to the car so you can have the center section line up with the end caps by sanding across the gap. then prime/block/prime using a guide coat till you're happy.

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Here's my tip for making a uniform edge where the spoiler flows into the decklid. A flat block with sticky sandpaper and a spacer to keep the block on the same angle as you slide across the spoiler. Don't forget tape so you don't mess up the trunk lid.

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I've now got both spoilers in final primer and will move on to other things. When I mounted them to do my sanding etc. I mounted the stock spoiler forward and the tall spoiler slightly back so that the stock spoiler would always cover any foot print marks, or fade lines from having the tall one. The tall version is about 1 1/4" taller than stock and mounted to the car in the pics below where it will stay a while so I can admire it while doing other stuff ahahaha.

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With the spoilers in final primer I moved on to mocking up all the pieces of the tail panel and bumper to get the best fitment, gaps, etc.

I had my bumper welded up to eliminate the bolts and jack slots many many years ago. I took a used bumper (no repros available back then) that still had the mounting brackets attached to it and sent it to a shop where the brackets were tack welded to the bumper, the bolts removed, plates welded over the holes on the backside, and the bolt holes plug welded from the front. Then the bumper was sent for smoothing and rechroming.

The bumper never really fit quite "right" due to the brackets being adjusted for the car it came off of and the ends had the side droop seen so often on 70-73's. So now was the time to fix things. I ended up making spacers and tack welding them to the bumper brackets to even up the gap along the back and modifying bolts and almost all the bolt holes so the ends can be adjusted properly during final assembly.

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This is the rubber isolator often missing on the center bumper support bracket. Held on by 2 plastic T clips.

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Here's a tip for masking off an edge you can't cut easily with a single edge razor. Rub a file on the tape.

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You can see the spacers tack welded to the brackets to create an equal gap to the tail panel in the pic below. Car had no previous rear end damage and none of the sheet metal had been replaced and although the bumper itself had been repaired and replated at least once before I ever owned it it's pretty straight. So I have to assume the fit wasn't very good from the factory judging by the thickness of spacers required and other 70-73 birds I've seen and dealt with.

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Back in the fall Holley introduced a new product at the SEMA show, the Holley Hydramat. It's a product that mounts in the bottom of a fuel tank and if the fuel in the tank touches any part of the Hydramat the fuel will be sucked in even if no gas is touching the rest of the hydramat. https://www.youtube.com/watch?v=yfE1v65fNZI

Holley started shipping about a month ago so I ordered one and got it a couple weeks ago so I thought I'd show it here. Will post about it again when I get it set up in the tank. Cost of mine was a couple hundred bucks. Seems expensive but to save the same weight (on track) with lightweight parts would cost more

This looked like a good product for me to try in my stock unbaffled gas tank until I can install a properly mounted and protected fuel cell. It'll allow me to save weight by keeping less fuel in the car on road courses without risking sucking air in high G corners, reduce the pendulum effect of fuel sloshing in the tank, be safer if there's a fire because less fuel in the car, and since it's also a filter I eliminate the canister fuel filter I've been using also saving weight.

I got the magnet kit for mounting the mat in the tank and will need to install submersible fuel line instead of the stock tube and sock strainer in the tank. Holley makes other sizes and shapes of the mat as well as types of mounting setups for tanks made out of other materials.

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Back in the 70's when we ran air shocks with big and small tires on F bodies I always noticed the crappy job GM did on the pinchweld under the rear splash pan because the rear of the cars were jacked up. Well those fugly looking pinch welds are still there on most of the cars and haven't gotten any better. They got bent on ice mounds in the north, rusted, repainted without being sanded smooth or stripped, and so most look worse than they did from the factory. I'm going to make a rear diffuser for my car and folks will be looking under there taking pics etc. so I figured now's the time to even it up and make it more presentable and finished looking while getting the whole tail section in final primer.

So I gave myself a guideline and used a 4 1/2" cutoff disc to cut a thin slice off. Then ground it pretty even with a 4" grinder stone, filed it straight, and got rid of the sharp edges.

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