This might rile som people, but I actually see Chuvalo giving a prime Tyson a lot of trouble. Granted, Tyson was much faster and more powerful than Chuvalo, but since Chuvalo would be always coming forward Tyson wouldn't get to fight at his favourite range (mid-range) as much as he wanted. He would undoubtly land some big punches, but Chuvalo's legendary chin might very well see him through those. And could Chuvalo make it a rough in-fight affair I think that his superior toughness, stamina and chin might very well see him prevail. At mid-range Tyson would be clearly superior, but he could he keep it there? I think he would have to end it within the first five rounds, otherwise Chuvalo would rough him up badly on the inside and maybe win by a late TKO or take a decision.
Tyson wide UD being tough and able to take Tysons punches does not mean that you will win. A great chin means a twelve round beating since Chuvalo has neither the style to negate Tysons ability to throw nor the hand speed to time Tyson and land consistently. Douglas and Holyfield beat Tyson by clinching and boxing not by coming forward and taking his punches.
Well, Holyfield beat Tyson through closing the spaces down, not letting him throw his bombs at midrange. Chuvalo would probably also close the space, trying not to give Tyson room. In close speed is not as a big an issue as it is on longer range. Holyfield showed that by keeping close to Tyson you prevent him from throwing his best combinations, that's exactly why I give Chuvalo a chance. In close Chuvalo's superior stamina might make the difference.
Holyfield was a vastly more talented fighter then Chuvalo . Chuvalo has the toughness but not the talent and skills to implement Holyfields strategy. You cant only clinch and close the space against Tyson there will also have to be times where you have to box Tyson and there is where chuvalo would fail Tyson would land practically at will and chuvalo has neither the handspeed nor skill to land on Tyson consistenly during the Times that he would have to box Tyson.