And if we'd keep going by ranking instead of by bracket set-up:
1. Ali vs. Marciano = that's tough. Ali would cut Marciano up, but the Rock would just keep coming. If it goes late, it would be tough to keep Rocky off, even for Ali.
2. Holmes vs. Tyson = Good style matchup for both fighters. Cus trained Tyson with fighters like Holmes in mind, and Holmes was a little slower than was Ali or Tyson. There would be lots of action, and both fighters have good chins. It would come down to a decision.
3. Lewis vs. Johnson = jabs and defense...I think Lewis' size may give him the edge, although Johnson did knock someguys' teeth out, which could pose a problem for the big man.
4. Louis vs. Liston/Holyfield = I still haven't picked a winner from the previous round, though either would make for a great fight with Louis.
This is insanely hard.