His career would look a bit a like Tommy Morisson's, i guess. A huge cannon with a weak chin. I don't see him beating either of Tyson, Lewis, Holyfield or Bowe unless he catches one of them on a big off-night. He'd mix up wins and losses with the (fringe) contenders of the day. Of the contenders/lower level champions, in my opinion he'd lose to Tua, Mercer, Schulz, Bruno, Ibeabuchi, both Klitschko's and Tucker, have 50/50 fights with Moorer, Stewart, old Foreman (Foreman was old and slow, but also durable and strong like Cobb),old Holmes, Morisson, Hide, Briggs. He'd probably blow guys like Weaver, Tubbs and Coetzee away in the 90's.
A fight between Shavers and Morrison or Moorer would be fun to watch. Or a fight with Mercer as well. Punch v chin. I don't think he seriously troubles the top four or five guys, but he'd probably do a fair amount of damage in the 2nd tier.
He can win against just about anyone, but I wouldn't give him odds in a few fights. Lewis would take him apart, I think. Shavers would have a punchers chance, but Lewis beat a lot of huge punchers, and I honestly don't see Shavers standing up to Lennox's heavier punches any better than Ruddock did.
