Mine is a '75 500 bored .030 making it a 507, you don't need aluminum heads, besides they are $3500. The '70 500 engine had 76 cc combustion chambers and around 10.1 compression. A good rebuild with the Edelbrock 2115 intake, a Holley or Quick Fuel Tech carb and a #10 cam from "Maximum Torque Specialties" will really set that engine free. Take a look at their website at Index
and also look at Cadillac Forum
, join the forum and see all kinds of big Cadillac engine builds.