Foreman would likely win, but Joe might have been a good exercise for him.. George could have benefitted from men who could linger around for a while instead of dropping face first after a barage of hits.
Foreman who fought Young was not awful, just not in the right mindset. That tended to be George's problem: his mindset. I see Foreman not having a mindset problem with Bugner and George would stop him within six.
Joe would have had his moments, but george would have caught him and finished him off like a junkyard dog devouring a sirloin in about the 7th round. 70's Foreman is one guy Bugner should be glad he didn't fight.
Foreman should win. His biggest danger would be punching himself out and gassing at the end. Bugner's style and durability may enable him to last quite a while with George. It would be a good opportunity for Foreman to work on boxing, pacing himself, and going the distance against a tough, though not a heavy-hitting opponent. I would pick Foreman to win a comfortable decision in 1977.