Re: How would a prime Charles have fared against Marciano?
Charles rose to the occassion for the first Marciano fight. It is often thought of as one of his best performances. Difficult to top that. From the footage that's available we see Charles staying off the ropes and using some fantastic upper body movement to slip Rocky.
Maybe 10 lbs lighter and a few years younger, Charles might make it a closer fight or his lack of mass and HW experience could see him perform worse. Either way, he's not stopping Rocky and he's not keeping up with his punch output for 15 rounds.
Charles was not himself in the second Marciano fight. He put on bulk and went out looking for an early knockout because he said he had no chance of repeating his first performance. He got badly hurt early by a clubbing right and lost almost every round.