This is a very interesting matchup. Both were very similar fighters. When George came back after the rumble in the jungle, he brought Gil Clancy as his trainer. Clancy's the one who slowed Foreman down, taught George to pace himself, relax. Clancy played a huge part in Foreman's comeback in the long run. This 1976 Foreman was very similar to the Foreman who made a comeback in the 1980s. The difference between the two, however was age and fat. The younger Foreman much more muscle mass and weighed less. He was also much faster. That's the difference between the two and that's why I pick 1976 Foreman to win this.
Young Foreman was a better all-around fighter but Old Foreman is a terrible match-up for him. Old George by a savage late round KO.
Wait, 76 Foreman? Yeah, this Foreman would have a much better chance. Although Young still managed to outfox him and get George to punch himself out. Could old George do the same? Much better match-up.
I agree with your pick, but win how? KO? TKO? I myself would probably pick KO. If Stewart rocked ol' George prime Foreman stops him.
Tko, I believe a younger George would've sent him down for the count. But this Foreman was to laid back.