keep the trans in mind...all things equal unless this is a hypothetical situation if you have a big block and are thinking of changing to a small block...everythings different...that can get expensive. as for power id go with the 383 they make gobs of torque, rev to the moon, you could find a set of closed chamber heads put bigger valves in them some mild porting and make a low budget screamer. I had a 440 with 67 lopo closed chamber with a valve job and bigger valves, stock short block a used fireball cam and iron sixpack and it put 400hp and 550 ft lbs to the pavement with a real conservative tune had 2500 into the whole deal with the sixpack 1200 into the engine and most of that was the headwork