Does your LS1 have fuel injection? I am not sure why you want to stay with the stock tank? Typically, most people upgrade to Rick's tank with the fuel pump inside. If you plan to have 3 inch exhaust out the back, then you need a narrow tank. My 67 Camaro has Narrow, Notched, stainless steel tank (with dual fuel pumps) from Rick's
http://www.rickstanks.com/ I saw one post on a guy modifying the stock tank. Well, I had one modified in the past. In 2000, I had to buy a new stock tank, and we had it cut and welded for sump. Then I had to have the stock tank tested for leaks. I was lucky in finding a local radiator/hot rod shop for leaks. I heard that it is hard to find a place to test the tank now. I had probably about $600 in that tank, but I think the best option now is just have Rick's build you a tank. There is several vendors on the forum that have the tank already ready to ship to you.
My car started off getting a frame off restoration on Rotisserie, but one of the first upgrades was mini-tubs. Mini-Tub is the most expensive option, because you have to get a rear end narrowed. Custom wheels for the 335's. I bought new NOS outers for mine, because I was replacing the factory quarters. Some Camaro's require new frame rails, but mine was solid. Rear suspension, do you want leaf springs or Quadra-link, etc. At the time, there was only the leaf springs and offset shackle kit. Although, I went to a Good Guy's show, and bought the quadra-link #1 (first one that was sold). Kyle agreed to take my never used leaf spring kit back. (Actually, most people upgrade to the quadra-link if they have leaf spring kit) Later we found out the Quadra-link test car was based on a 69 Camaro. The 69 Camaro is a few inches longer, so just say that mine was moved more than once. The advantage of doing a frame off restoration, you will find sheet metal that needs to be replaced. A friend of mine was building a cruiser car 69 Nova, and I told him that most likely the subframe mounting points were rusted out. He kept telling me they were fine, but he never checked. Anyway, they pulled the subframe out of the car and found they were rusted out.
The original plan for mine was to use the stock subframe, but then DSE brought out the front subframe. So, I upgraded to that as well. If you are following Camaro XV, then you notice the new motor mounts that Mark has put on his car. Mine has that as well, because I am in the same shop. Reduces vibration and noise. I always liked the Fiske 5S, so I have no plans of changing that option.
The brakes I used was Baer Extreme+ 6S brakes, they fit the C6 Spindle. The DSE subframe has Corvette C6 spindle, so your brake system has to match your spindle. I am not sure if the Brembo Gen 5 brakes from the Camaro will work on your subframe. The old method for the subframe was to use an adapter, but I sold my Alcon brakes long ago.
My rear end is a Currie 9", but I had that in the past. My old engine was 383 SB Chevy full roller with around 612 hp. (Turbo Blue) The engine would rattle the car, but it was built primary for drag racing at the time. I hated that engine because of the vibration. I planned to upgrade to LS engine, but I made the decision to do a supercharged engine. This upgrade causes you to upgrade several components, but depends on the horsepower/torque. Anyway, the street manners of the engine is like a stock engine, with lot of torque as you press down the pedal.
Vintage air, dynmat, etc. Really it depends on what you want for your car, but the first thing you need be sure that it safe to drive. So expect lot of sheet metal to be replaced. I owned my car since 1983, so I know most of the history. When you take the car apart, then you find out more things about the car.
Jeff
PS. Hid Lights are illegal in most states, but varies on the state. DSE has these bright lights, but not an actual hid. The other option is LED lights, but most of the LED lights won't work with RS option. Not sure on 69 Camaro, but they are to thick for 67 Camaro RS.