The 390 is one of the very best engines Cadillac ever made. It was the last of the series of engines used in Cad and Oldsmobile from the late 1940's to the early 1960's, ones designed by the legendary GM engineer Charles Kettering. If the engine is still able to turn, I'd suggest trying to get it running- - - -its condition might surprise you. I've got a 61 Cadillac 390 sitting in a motorhome my father spent many years building from a Cadillac hearse chassis and a Spartan aluminum-skinned mobile home. Dad's health failed and he never got his project on the road, but I haven't been able to make myself haul it off to scrap. He put a huge amount of work into it, including doing a massive amount of dyno run time on the Cad engine. He adapted a Quadrajet carburetor to it and jetted it for the full range of performance, from idle to wide open throttle. The torque numbers were impressive!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!