Leonard wasn't that effective when he had to press and lead the action, especially against elite opposition. I think he would probably take duties as the outboxer in this one, where he was more successful. Good analysis of his defense. He was clearly capable but never truly looked like a slick boxer in there. Perhaps it's down to defensive responsibility and awareness than ability.
Gavilan was extremely durable and one of the few fighters never to have been stopped. He was a competitor who could fight anybody but I have to go with Leonard for sure in this matchup. Leonard had a better boxing brain and could think and adapt better. He had more to offer overrall. Gavilan struggled against Billy Graham who was really a stand up straight boxer, much slower than SRL. There were guys that beat Gavilan. Danny "Bang Bang" Womber was a big underdog and beat Gavilan. If he could do it, then so could Leonard.