Marciano gets off the floor to grow stronger as the fight goes on and starts picking up the pace and putting on the pressure from the 6th rd on....Marciano by KO in the 10th
This fight would take place mainly on the inside. Therefore Marciano's lower center of gravity, shorter arms and superior stamina gives him the edge here as I see it. Speed wouldn't count as much on this distance. Neither let loose volleys like for example Ray Leonard when infighting, to put it mildly. By all accounts Rocky also has the edge in power and chin. He had more impressive KO's over strong opposition (say what you will of the age of Louis, Walcott, Charles and Moore - they absolutely **** on the likes of Willard, Firpo, Brennan and Carpentier however you slice it) and he wasn't KO'd in the first by a someone like Flynn.
Been reading some opinions on Dempsey MIke Casey the historian rates him number 1. Max Schmeling rates him number 1. Gene Tunney rates him number 1. Jack Sharkey rates him number 1. Ray Arcel said he would "absolutely beat every one who came after him", including Marciano,and Louis ,whom he rated number 2.
You just do not appreciate the art of swarmers fighting from a crouch... dipping the torso at athletic unpredictable angles, slippng ducking punches by rolling around or bending out of range...always leaving his opponent off balance when he misses. Marciano knew how to fight short, it was a great strength of his. this is why the taller bigger fighters of future generations would have so much trouble with him. They never fought a smaller fighter with the style and tools of Marciano. They would find him terribly ackward, and hard to hit cleanly in that low crouch. It would cause them discomfort. Marciano would feel at home working his way inward and punching upwards, while unless they had a strong uppercut they didnt have much to offer punching down. Angelo Dundee himself said "Charlie Goldman made Marciano into a cutie"
All I know is it would be an epic epic fight. Not one that I would like to see tho as I like both fighters alot.