1975-1976 caddy 500 was only rated for 190 hp.
1970 caddy 500 was rated for 400 hp.
If you are using a stock motor, it would be better to use the earlier motor. If you are building one, there are Stage I kits that will make 500 hp with 550 lb/ft torque.
If the stovebolt in question is a 1958 gmc, I would reccomend the 1959-1960 Pontiac 389, as they will bolt in to a GMC chassis with no fabrication. Use a stroker crank from Butler performance and you can make 447 or more cubic inches.
