What`s the heaviest a fighter can way and still be able to win the heavyweight title?

There is no limit.

 

325lb.

 

dpends what set of rules and kind of boxing.
high tempo 15 round bouts, giants are severely disadvantaged.

shorter bouts with low output, giants have a better chance of using weight advantage.

 

If they changed 20x20 ring size to 75X75 they can!

 

Old Foreman was... old? Yet still looked better than Ruiz easily. He doesn't train road work and eat a lot. It's easy to see that he does? Haha, no, it's actually the opposite. Like I said, he might train hard in sparring and the bags and other skills and coordination things. But he doesn't do a thing to lose weight. 0 diet and 0 or barely any road work.