I have one of those Pontiac bell housings too. If the right flywheel were easy and cheap to come by I might put it to use behind a Cadillac but not this project. I actually have two 500s and a 472.
The '70 500 was the highest rated of them all. Two things happened over the next few years. The compression was dropped and the horsepower rating system was changed. More of that drop is the result of the change in rating system than the lowered compression.
There are basically two sets of heads. The earlier ones have smaller chambers and flow better than the later ones. My '76 motor is the last year the 500 was offered, it has the HEI and larger chamber heads. It also has only about 70,000 miles on it.
Based on my research an intake manifold and cam change will bring back more than enough torque to do the job without requiring turning the motor more than 3500 RPM at any time. There is no substitute for cubic inches.
The project isn't finished yet so I have no experience of my own that proves this will be satisfactory but I'm optimistic.
