I like using a late 70's Trans Am sub frame, not just a regular Firebird. The T-A has heavier sway bars, big rotors and a quick ratio steering box. And if you car find a parts car look at the GM 10 bolt under the rear it may have disk brakes. That would be a double whammy!
Then grab the brake booster and your set.
Also the Pontiac motors were big blocks so the spring can hold up pleanty.
Just my .02 cents. Hope it was helpful.