John L Sullivan vs the all time great heavyweights.

Although I thought that Ali would be one of the tougher opponents -- if JLS was fighting him in ALI's day -- I do think that JLS's time would make some difficulties, too. So i think kurgan has some valid points.
Now, if you imagine an Ali-type fighter born into Sullivan's day, his technic/style would be more appropriate to the time. However, I do think that the 1960's-70's jibe with Ali's native endowment better than the 1880's.

 

Completely speculative of course but I would expect the post-Marciano fighters to all beat him in extremely one-sided matches.

 

I'd pick Sullivan to defeat Charles and Patterson, and would give him a good chance to defeat Johnson , but the rest of the matches I think he's an underdog.

Essentially his power gives him the best chance against less than stellar chins vs men close to his size or smaller even if his skill set is lacking.

 

Nelly Bly published a pretty good detail of Sullivan's training for Kilrain, and the mention of his feinting (which we can see on film as he fools around with Corbett prior to Johnson-Jeffries) brings to mind Bob Pastor's report to his corner early in his first bout with Louis that he could feint Joe into knots. Pastor was no Sullivan when it came to size, stamina, punch resistance and punching power. The Boston Strong Boy's feinting could then be critical in dealing with the Bomber.