MM was beastly as a light heavy but completely unproven. No way you could pick him against a legend like Archie Moore. Archie was basically finished at heavyweight. He was cagey enough to provide Moorer some problems but comes away the loser.
The Old Mongoose knocks MM out at 175... Catches him with some sharp counters and gets him out eventually At heavyweight, Archie had some real good results because of his great skills and his ability to still carry power at the weight, but he was also more vulnerable to punishment up there... For Archie, getting to 200 was about as far as he could go and still be a functionally good fighter... Moorer was able to bulk up considerably and didn't look out of place in a heavyweight era where the average top flight guy was well into the 220s plus... Archie Mo' still had the savvy to capitalize on a MM mistake and had enough pop to hurt him, but I don't think he could handle what was coming back... At heavyweight, it's Moorer's fight to lose
