You forgot Audley Harrisson. He'd win a mini tournament with these guys, too much guile, craft, and a solid chin for these guys to compete with. Audley takes all.
At amatuer level? tough to say. The rules of amatuer boxing have changed so much lately its not funny. Chris Byrd beats them all, unless they get a stoppage.
Stevenson was one of the greatest heavyweights ever. I don't think there is anybody he couldn't have beat. Too bad ****-brain Castro kept him in Cuba.
Most probably they haven't seen the other fighters mentioned fight in the amateurs. Again this is the amateur friends . . . do you guys even saw "Cassius Clay" in the amateurs?