Quarry struggled a lot with good boxers given by his performances against Patterson, Ellis and Machen. Johnson had the right set of skills to get through this and did have success at heavyweight so he wasn't going to wither in case Quarry landed some shots. Using the afforementioned Quarry performances and then looking at Johnson's success against an elite counter puncher Ezzard Charles, Johnson should win the decision. Just hope this doesn't go the way of the Walcott or Moore fights, but Quarry didn't have the skillset of those guys.
Chatgpt favors Quarry. Personally I can see Quarry winning, but also see Johnson out boxing him. I’d favor Jerry Quarry over Harold Johnson, roughly 60–40. Johnson was the cleaner technician: excellent jab, compact right hand, good defense, very disciplined, and one of the best light heavyweights of his era. He could absolutely outbox Quarry for stretches, especially if Quarry got impatient. But Quarry was a natural heavyweight, usually around 195–200 pounds, and he was very good against smaller men who came to him. He had sharp counters, a hard left hook, and enough physical strength that Johnson’s usual light-heavyweight advantages would be reduced. The key issue is size. Johnson was generally around 175–180 pounds. Against Quarry, he’d be giving away perhaps 15–25 pounds to a man who was not just bigger but also skilled and experienced against elite heavyweights. I’d expect Johnson to win early rounds with the jab and straight right. As Quarry gets his timing, though, he starts countering Johnson’s entries and working the body. Johnson was durable, so I wouldn’t automatically predict a knockout. Most likely: Quarry by competitive decision, perhaps 9–6 over 15 rounds.