Stylistically this would on paper be an extremely tough fight for Ali. Could go either way. Larry Holmes would also be a nightmare for any version of Ali.
I would give Steward trained Wladimir a fair chance to beat any version of Cassius Clay/Ali. Stylistically the match up favors him. Throughout his career he has never had a problem against the smaller, quick featherfisted stick n runners. Earlier in his career he had some defensive, overpacing issues that flared up against some big punchers but they were sorted out under Steward. Ali had no answers for Ken Norton's jab and I see him struggling mightily to get by that lead jab/left hook. Alot of holding and clinching from the bigger man can sap Ali's strength. Wlad won't waste energy throwing wide, frivolous punches like Foreman did in Zaire(wtf was he thinking?). With fair, neutral judges I'd say Wlad beats Clay/Ali by decision. Ali got many gift decisions in his career so Wlad could get robbed as well.
Ali was put on his ass by skinny light heavyweights and morbidly obese cruiserweights who couldn't even punch straight. Ali also had a terrible workrate, barely throwing anything for entire rounds, and was extremely featherfisted. His technique was beyond terrible, he did so many mistakes, unbalanced, open, throwing pit-pat-flurries on the tip of his feet, his jab was lumpy and most of his power punches were arm punches. He based his style on being much bigger and heavywer than his average opponents. At his times, he was considered a giant, while he was merely a 6'3, 215 lbs. It's not wlad that would beat him. Any top 50 today would have a good chance of stopping or schooling him. Ali would barely be a sparring partner, today.