Ali at no time in his career "toys" with Marciano. For any Ali this would be a very stern test. Prime Ali wins by decision. The Ali who fought Foreman is "pickem" bad prime Rocky. A crouching weaving tough as nails two fisted ko artist who can fight 15 rounds and not get tired would be a difficult opponent for an older Ali who could not move 15 rounds.
I initially posted this as a 50/50 fight, but funnily enough I've just watched Ali-Foreman again, and for me Ali has to be seen as a firm favourite.
I agree. Al has got to be the favorite. To me, this fight would go down like it's pseudo documentary movie aptly named "Rocky". Creed, a past prime but great Ali against a prime Rocky Balboa, err Marciano.
A great fight ! Ali would definitely be able to move more than he did in Zaire because Rocky would n't be able to cut off the ring like Foreman did. In turn,Muhammad would spend as little time as possible on the ropes as Marciano would do more damage than George was capable of. Ali wins. Probably by a hard fought decision unless Marciano gets cut so badly forcing the referee to stop the bout.
Problem in Zaire was not just Foreman ring cutting. First it was a smallish ring with a thickly padded canvas. Brutal for any boxer to move on for any length of time.