This is one of those few occasions, size would not matter.
Wladimir is 6'6, Ali is 6'3, three inches is not much.
As for Klit's muscle, I think that would be a complete disadvantage. Ill explain why.
First Klit is not going to win the jab game against Ali, He has gotten very comfortable fighting guys much smaller and not having to move that much. There is a reason for that, his conditioning is horrible. He has gassed himself out in fights tragically when he is put in a position he has to punch.
Ali by comparison at his prime could move much faster and smoother...he would keep the fight at a pace Wlad would NOT be comfortable with. Wlad would know he is losing rounds in the outside jabbing game and be forced to follow a dancing Ali around the ring trying to make up points or get rounds. Under those hot lights and at Ali's pace Wlad would be gassed out by rounds 5-6.
And right as Wlad started sucking wind, Ali would start turning that devastating right hand over, catching him in the mouth. Now lets be honest, Corey Sanders (RIP) a full time bartender part time boxer, slammed Wladimir all over the ring.
Wladimir would be defenseless against Ali by round seven and would get brutally dropped.
A 1965-67 Ali TKO's Wladamere with a Cut or a close but decisive points decision.
The only version of post war Ali that has a good chance is 1974 Ali.The version who trained himself into top shape for the Foreman fight
i'm going to get slaughtered for this but i think wladimir would give Ali a good fight ,Ali at his prime was by today's standards a cruiser weight weighing some 40 pounds lighter than wladimir .look how easy both klitschko's have dealt with former cruisers who have moved up to heavy weight like herbie hide ,david haye , jean marc mormeck & adamek ,now i know these fighters aren't in Ali's league but the size difference is huge and i see it as a close fight with wlad keeping centre of the ring as he did against haye forcing Ali to take pot shot but getting outworked at times from distance Ali would have dominate spells but so would wladimir using his long jab , wladimir wouldn't punch himself out like foreman or be as slow as liston he would be more like norton who beat Ali but bigger and stronger .remember Ali was quite a lazy fighter who didn't like being forced to fight at a high pace by frazier & norton and i think wladimir would do the same thing .
as for the result i see one of two things happening either wladimir by points or Ali by late ko .
Wlad cannot IMo fight going backwards proven by Corey Saunders for one. Ali shuffles, throws endless combinations and then starts overpowering Wlad that can't get set to get off.Ali scores 8 round TKO.
the klitschko's are good and their respective accomplishments have to be commended, but ali was superior to them in everything but size and power. he outpoints either.
ali wins easy
Both men at their best, fighting 15 rounds for the heavyweight title. Who, how, when, and why?