The Cooper from the 1st Ali/Clay bout, circa 1963, vs the best version of Quarry, 1967-1970.
12 or 15 rounds.
Personally, I see a nice classic Slugfest, for at least the first few rounds. They both had issues, pertaining to getting cut, Badly, and early. Even though Cooper might floor Quarry, with that lethal left hook, I see Quarry's iron chin and jaw withstanding Cooper's offensive barrages en-route to an eventual later rounds tko, likely in the 10th, imo.