Not sure he would have beat Marciano, I would give Rocky the benefit of the doubt just because he never did loose.

He would have beat Archie Moore,

Michael Moore (the fighter lol)

Frank Bruno

Buster Douglas

And the best fighter he might have probably beat is Big Daddy Bowe, I actually think that would have been a very entertaining fight.

And for the record I think his brother is better than him and would have beat or at least stood a decent chance against a lot more atg's than he would have.