As strong and sturdy a fighter as Vito was, Fullmer would have been way too resourceful, and too strong for him. It would have been similar to his two maulings of Carmine Basilio. Vito would have been tko'ed on cuts before he got completely outmauled. Fullmer was gloriously dirty and rough and would have been a nightmare for Vito. Gene would have used the same "Plan B" on the rather limited and unimaginative Vito that he used on Basilio.
My only issue with this eval is that I believe Fullmer fought in plan b mode against Carmen. I believe he's on record as saying... why try and out tough Carmen and rough him up, when I could outbox him a lot easier. He purposely didn't engage in his usual rough swarming style against Carmen, some I'm not so sure he'd try that against Vito.
I'd go for GGG too mobile and hits a bit too hard for Fullmer to charge in recklessly.I never thought too much of the Mormon.