Yeah, I think many forget about the "build a better airpump" theory. Good compression is there in ALL rpm's ranges and the 516's nominally smaller porting may actually create a higher velocity port too. Especially for the 383/400 bore stroke combination.

Low compression seriously hurts low end with a 230+ duration at .050 and the 383/400 is a relatively short stroke motor compared to any other big block and even a 383 SBC.