Liston prime by a brutal KO in the 5-6th rounds.He would have closed the distance easily. If it's Liston 66-69 version he will lose by unanimous decision against Holmes, He would be kept at bay by Holmes' quick jab.
Liston. More skilled than Mercer, better jab, likely hits at least as hard or harder. Middle aged Larry isn't weathering that storm. Stranger things have happened, but I'd be very surprised.
If we're talking prime Sonny then the ref would be stopping this to save Holmes from himself. If we're going old to old versions id take Holmes