Povetkin would be koed easily by every single one of them, that's if he wasn't banned for ped's before the fight happened!
Povetkin would beat all of them except "prime" (before he was shot and punch drunk) Ali, modern boxers are just on a different level than most of the greats in the past. He's technically more sound than any of them and also bigger and stronger.
This, fact is VADA testing did not exist during their times, they would probably test positive for PED's as well had they went through VADA testing.