I think Primo Carnera would be a pretty tough proposition for Floyd Patterson as it was. Let alone with a a trainer like Manny Steward in his corner. I'd probably go with da' Prim'.
Steward knew how to train tall guys and a simple jab and more fluid movement would be to much for Patterson,whos chin would never hold up.If Patterson was better than he was he would not have avoided liston as long as he did and he knew a big puncher would k.o him.Carnera would hit hard enough to k.o him without question.
Primo Carnera often had a pretty decent pair of trainers in his corner by the names of Whitey Bimstein and Ray Arcel. He wouldn't need Steward. Patterson was a better fighter pound for pound but Carnera's got the size and weight to pose a real threat to Floyd. Not sure Floyd can win this one. I'd lean towards Primo.