A complete mismatch or possibly a stylistic advantage that gives Primo a real shot .. This was the four or five rounds and out Foreman, who was mentally weak and did not master stamina and pace v.s. a Carnera who had tremendous heart and that only a lightning fast murderous punching Joe Louis was able to stop early .. could Primo use his jab, re-cooperative powers in addition to his own physical strength, which may have been close to Foreman's, to survive the early rounds and outlast Foreman ?
Result is era dependent. In any era Foreman is a favourite but the later it gets the more chance there is of the Italian being stopped by a nervous referee before he takes advantages of the weaknesses you describe. But I guess probably Foreman gets him out of there anyway. World class offence early. Baer took ten mind. Might be long enough.
I think Foreman probably batters him to the canvas enough times to force a stoppage. Carnera might have his moments, and might take some rounds, but I doubt that he springs the upset.
I can see it going 2 or 3 rounds...no more than 4...today's refs wouldn't tolerate multiple knockdowns like in the past. Foreman wins by tko after Carnera goes down a few times. Primo would make a particularly brave stand and would be successful in warding off Foreman's attack using the natural advantages mentioned already, but as I said, a couple more kd's and the ref would have seen enough and stopped it. I think Primo's strength was probably equal to Foreman's, and his boxing was slightly above average, but the Italian's courage would have done him no good ultimately. George showed that he was good at slaying giants, as in his pre-title blow out of Jack O'Halloran. My first point about multiple kd's not being tolerated would apply to Dempsey-Willard if that fight were held any time in recent decades instead of 1919. Dempsey would have been a quick first round tko winner over Big Jess.
Cant see Primo seeing 5 rounds. Brave guy that he was, George drops him a few times to force the stoppage. In fact, RC above said it better than me
prime primo was much braver and tougher than you think, he might well go the distance with big georgie, and would likely beat ol georgie.
Look, Primo was in be of the few who could tie George up. Very strong. He had a decent jab and reach. He survived early blasts from Baer. It's possible he could tire George out.
I have defended Carnera as much as anybody here, but I feel that he lost to the very hardest punchers of the division. He beat lots of punishing hitters, but he didn't beat anybody with Baer or Louis type power, or even somebody who had sick power and not much else. I have to say Foreman.