Lewis doesn't stop Ali when he could still fight. 76-80......that's a different story. Ali's last fight where he could fight was Ali-Frazier III.
I thought we were talking just 74-75 in general, that time period. If we were talking a late 90's or even a 00' Lennox, I'd say he beats a 74-75 Ali. But Lennox wasn't much at the point of the Vitali fight. He still had his power, Ali could handle power though. Ali also would still have a noticeable speed advantage, even at 32-33 years old. I'd favor Ali by a close and competitive decision.
It's all opinions though.