Razor Ruddock is the obvious favorite here. A fit Kirk Johnson could potentially make this an interesting and dare I say, competitive match, but I'm not sure that I see a strategy that would make him a winner. The Donoven Ruddock who lambasted Dokes in 4 rounds, then took Tyson 12 in a respectable losing effort was definately a force to be reckoned with, and not one that I can see Johnson over coming.
Damn...that video brings back some memories. Physically, Ruddock had it all: Large size, quick hands, good chin, monster power with the left, 82" reach, athletic... He fought stupid though, which sometimes was his downfall; winging punches leaving himself wide open, under-using his jab, (which was pretty good actually) and sometimes was too square when throwing the right. He was game as hell though, and always came to fight. He never backed down from anybody. I'd love to see him in his prime fight Wladimir.
Ruddock was basically a one armed fighter. Used very little else than his left. He would still kill Johnson though.
Ruddock flattens a fat Johnson in 2. Ruddock flattens an in-shape Johnson in 4. Either way Razor leaves him for dead.
The fact that Tyson took Ruddock's best bombs for 2 fights, and smiled at Razor all the way through tells you how good Tyson's chin was.