I think it would be an amazing fight. Like they always say styles make fights and you don't get anymore opposite than Ali and Marciano. I think it would resemble the Ali vs Frazier fights with Marciano getting in good shots and pressing the action and Ali landing quick combinations. Marciano is very similar to Frazier with better stamina, chin, and a better right cross. It's hard to say who comes out on top, but I think that its an awesome match up and would be even more exciting to watch then Ali vs Frazier.
Ali would win the early rounds by dancing and moving and using his speed and reach advantage. Rocky would catch up and get better success in the mid to later rounds. Ali comes back on strong in last few rounds. Ali by UD. Rocky has to get real close to Ali for success and this is best by cornering Ali. No one cornered a peak 60s Ali unless it was in a computer match set up by someone named marijuana oh soz murray warner.
I have this gut-feeling that Ali's jab would cut up Marciano. It always pops into my head whenever I think about this matchup. I read a quote by Henry Cooper once who put it this way;'he drags your flesh.' (referring to the fact that Ali punches away from himself when jabbing)
It would be a simular fight to Ali/Frazier 1 but I think having Ali hurt in the 11th rd. and on,Marciano's pace,beatings to Ali's arms and body,neck,shoulders would take there toll on Ali,Rocky may be swelled up and cut but he would be relentless. I dont see Ali making it to the end of the 15th. Joe Frazier said himself the only other 2 heavys that would beat him were Marciano and Louis, he said it would be a bad mistake for Ali to rope a dope Marciano. IMO anything can happen with men so great in the ring but I see a Rocky Marciano victory
Ali himself should have some insight into this because he sparred with a 44 year old Marciano. I think he came away with certain impresions. 1. That Marciano would have given him many of the same stylistic problems as Joe Frazier. 2. That Marciano was awkward and hard to hit cleanly. 3. That you only had to expose the tip of your elbow to Marciano and it would hurt the next day allong with the rest of your body.