I have never seen a fighter look as 'shot' as Ali did that night. Some fighters get knocked out in 2-3 rounds and are shells of what they once were mainly based on poor punch resistance. But with Ali lasting 10 rounds we really got a good look at his physical deteriation over the course of the fight. He was competitive for a round, then he suddenly looked like an old man who could do nothing else but try to defend himself.
He'd do about as well as he did against Holmes. Swift feet & fast cobinations were too much for Leon.
How the Ali - Holmes fight was even sanctioned is a mystery to me. Ferdie had quit him several fights before....and you could see Ali was shot and had been pounded even by Spinks with a grand total of 7 pro fights. Then he comes back after 2 years and is thrown in with Holmes at his prime, and used as cannon fodder. Ali's management should have realized what was going to happen...and it did.
ALi in his prime would have beat any heavyweight who ever laced them up, period. Prime Leon beat an old, out of shape Ali, and a prime Leon would lose to an even older Ali in the rematch 7 monthe later. SO if an old Ali can beat Leon at his peak, Leon would have a real tough night against prime Ali.
Ali would beat Spinks in about six rounds on a TKO, with Muhammad flooring Leon three times.Only way if Spinks won any rounds if Muhammad let him win.
Leon would make it lively enough for three or four rounds. After Muhammad finds his range,though,he stops his man before the seventh. Even the 1974 model would convincingly beat Spinks.