Speedtech sells that T56 tunnel which can be installed with screws etc if you don’t want to be welding on your car.

Installed this on my '68 that has a SBC and T56, I did the cutout with the finished interior, so welding wasn't an option and used 3M panel epoxy. Pain in the ass...yes, wish I had a garage that wasn't built to barely fit a 1920's car.

I see first gen tunnels. Not second.

I went with the 4l60 because they said a 6l80 would definitely require mods. I would’ve much rather had the 6l80.

Sorry. I’m stuck in first gen mode. It can likely be adapted to fit a second gen.

The reason I went with the 4l60 is because Speedtech said with that trans, I would not need to modify the tunnel like I would with the 6l80 that I preferred.

I was willing to go with that trans to avoid any tunnel work.

A CV driveshaft isn't recommended by two different shops I asked to hopefully avoid the angle issue. Both said the weight would cause transmission damage due to this.

Did you ever figure this out?

Sort of.

Donny (in this thread) took care of the tunnel and corrected the angles.

The car feels much better with my limited drive time-hopefully much more in the coming weeks.

Unfortunately, the noise (whine, hum, etc.) is still there. I believe it's slightly quieter but definitely not gone.

The noise is the most annoying part. Some background on the axle/center section:

Dutchman originally supplied the rear axle as specified by Speedtech:

It’s a 31 spline Eaton TruTrac with 3:70 gears, nodular iron case, aluminum Daytona style pinion support.

Everything went together easily and without issue. Upon driving it, it immediately exhibited and increasing in volume hum upon accelerating then decreasing as it slowed. The noise is not affected by trans gear and is by vehicle speed.

I contacted them and they asked that I send the center back. I did and they couldn't find anything wrong but changed the gearset to anther ratio (at my request) and brand. No change.

Dutchman and Speedtech claimed there should be no noise. The previous 10 bolt had none. The only change was the complete rear axle assembly and driveshaft. PST made the shaft. It was also sent back to be rechecked which yielded no issues found.

Dutchman kept blaming the transmission. The noise seems to be behind me and not under nor in front.

Researching lead me to John's Industries. I contacted them right at their acquisition time by another company. They were willing to look at the rear and suggested a different gearset. Off it went for a new gearset and rechecking of everything. Back it came and no change in the noise.

I kept asking if we could swap out the TruTrac and warranty it as nothing else affected the noise. Dutchman refused and claimed TruTrac's can never go bad nor make any noise. Never is a strong word and my luck with this car likely makes that improbable.

Strange is local to me somewhat. I decided to ask them about the center and if they could take a look at it.

They also swapped gearsets and a couple of other parts. They could not swap the TruTrac as a warranty claim and did not find anything wrong with a physical inspection. Back in it went and little to no change.

When I described the noise to Strange (and later Moser who I saw at a car show) they both blamed the solid mounted torque arm set up and more often than not, inherently noisy 9" rears. Both called it a tuning fork suggesting swapping either to another rear or find a way to isolate everything with rubber. I'd like to try the rubber but there is no way that I can see without quite a bit of reengineering.

After the center came back from Strange, it went to Donny's shop (definitely recommend his place if you need any work at all) for the tunnel and angle work.

At this point, I'll try and live with it for now or eventually try one last thing-swap the TruTrac for a Wavetrac. The angles are now correct after the floor work but if this was going to be the case al along, I'd have much rather had the 6L80e than the 4l60e.

Been chasing a similar issue with vibes and angles. What angles did you end up with? I tried pinion down, pinion up. Trans is down 3 degrees, drive shaft up 1 degree to the rear. Front of pinion up to the floor 2.5 degrees. Vibe is better but not gone. Triagulated four bar. Sucks to move pinion angle, because I have to put it on alignment machine to get it square again. I have a 9" with a locker in it. I had a TKO in it, put a TKX in it to raise up the trans from 4 degrees down. Didn't think I needed to do tunnel work when I built the car. 2.5 to 3 degrees down I thought was stock. Had some noise from the TKO, still have some from TKX, might be from the rear I guess.
Thanks for the response.

9" rears and aftermarket gears make noise. Some worse than others. It's why some guys are going the Ford 8.8 instead, trying to reduce the noise. If you can find a set of good Ford gears you'll likely get the best result regarding noise. I'm hoping mine is on the quieter side.

I would take a look at Detroit Speeds 8.8 inch in 9 inch housing center section. I considered it for my 57 Buick wagon but decided to try a 9 inch because I already had axles. I think you need to change out one axle. Definitely worth a look imo.
https://detroitspeed.com/products/re...nter_sections/

I’m sure Donny can offer some feedback on it.