A good big man would be too powerful for Rocky Marciano, they would keep dropping him, cutting him until the fight is stopped similar to Frazier-Foreman.
I believe Vitali Klitschko, Wladimir Klitschko, George Foreman, Primo Carnera and Jim Jeffries would all do this to Rocky.
People think it's controversial that i mention Carnera, but Primo was 270lbs of muscle, he was 6'6'', had a reach of 85'' and he had power.
Rocky would knock Vitali into unconsciousness. Rocky won all 49 of his fights and 43 were by KO. No one could figure out how to beat Marciano.
Vitali by decision or stoppage. Rocky is really a light heavyweight or cruiserweight. That is too much of a weight diff to give away to a skilled giant who is also an all time great.
Sometime during that fight, the undersized Marciano lands Susy Q, and the fight is over
Who do you see winning this dream fight.