It's hard to dictate George's prime. Now that I think of it, I think I would make a young George and an Old George about an even money fight.
Young George, yes. Old George, no way. Old George was perfectly matched up and all opponents were hand picked for a reason. Liston doesn't have any of those reasons.
Hard to tell. Maybe, the young George would blow away Sonny. But Liston had the better basics and maybe, he would weather the storm to put away George in about five rounds. Now, who was the faster (make it "slower") of the two? That would be an interesting question.
Mighty Joe Young ain't beating King Kong. Foreman would have serious problems. His power is matched. His physical strength is matched if not exceeded. Sonny would probably dominate Foreman and then put him away with a boom and a crash late. Old George? He would be unlikely to fight him. Let's not forget how calculated George got with age. If he did fight him, he would get seriously cut, seriously swelled, and probably seriously hurt. What Stewart and Moorer did to his face would seem merciful. And there would be no sudden shot to end matters here. I think that 1959 Liston is the bogeyman under the bed of 1973 or 1991 Foreman.
Liston beats any version of Foreman, he was the better technician by a distance and and ring general too. They're equal in terms of power and durability. Liston: TKO9.
Again I would have to say that Liston is the perfect stylistic foil for Foreman. Those wide open swings would be punished brutaly.
Sonny Liston would have beaten George Foreman. I think George had better power but Sonny could hit and had better fundamentals. While it could conceviebly go either way I'd give the edge to Liston.