65-67 GTO
64-69 Chevelle
65-66 Mustang
67-69 Camaro
Lots of great over the counter parts for all of them. Those are all pretty easy cars to restore / customize, although the GTO is gonna be a bit pricier.
I like the GTO body, and would probably put a crate 572 in that with a built turbo 400 behind it.
I had a 67 GTO convertible years ago that had been in a wreck. I bought it from the firewall back, which was in good shape, then put a 454 and a Turbo 400 in it. I got a salvaged front clip from a wrecking yard, then had the car painted screaming yellow with a black top. It was awsome.