Frazier, as great as he was, was very one-handed - all his power shots came from his Left - left hook to the body, left hook to the head.
Whereas Rocky had KO power in both of his fists. I would also say that Marciano had a better defence than Frazier, he was difficult to hit with the jab (as Ali said himself in 1970/1 when filming for the Superfight between them) and Marciano had probably the greatest engine in boxing.
So yeah, looking at it all... Everything points to a Marciano victory for me.