Would be a helluva fight, akin to the Ali-Frazier bouts.

Both are elite level heavyweights with clashing styles. Marciano being the pressure fighter and Ali a pure boxer. Ali had problems with guys who could pressure and pursue him and Marciano was cut prone ... Ali's stinging, dicing punches would definitely leave more than a few blemishes on his face.

Both have good durability, plenty of heart, stamina, intangibles etc.

I think Ali would more often than not win the boxing match, but "lose" the fight. Meaning that Ali would win on the scorecards but take more damage overall.