I would go with Ali by decision since Foreman showed good stamina and learned how to pace himself the second time around. Ali was in great shape for Spinks 2. It was his last good fight so I think Ali would have outboxed the game Foreman here.
Ehh................... For the sake of this being the Classic Forum, let's make it a 15 rounder. (It's funny though, that the "prime" version of George never even fought a full 15 rounder, even though he was scheduled to fight 15 rounders five times)
The Ali of New Orleans had the legs to stay away from Foreman for most of 15 rounds, and remained tough enough to take it when George did connect. This would be an uneventful UD for Muhammad.