Nunn via one sided decision. He is one of the worst match-ups that are possible for Duran. A tall, slick, rangy southpaw with quick hands, quick feet, & an elusive, spoiler style. His physical attributes are similar to Hearns - just minus the power, which is why I see Duran going the distance, but looking bad throughout the bout & barely winning a round.
Smooth lengthy boxing seems to be Duran's kryptonite (at least based on Duran's bout with Hearns and second bout with Leonard) and Nunn basically like watching butter melt in a pan whilst in the ring. Plus the awkward style with him being a southpaw mixed with his footwork and amazing punching angles, I might have to say Nunn wins this. Plus the man is huge, Middle, Super Middle and Light Heavy? Duran is a savage, but Nunn is naturally bigger and still as slick as the best of them. Me personally I would wonder how Nunn would do against Hearns, but we all can't get what we want. lol.
Controversial opinion but I think Nunn beats Duran, Hagler of 87, and Leonard of 87-90, I think Hearns beats Nunn though. Boxers didn't trouble Hearns he was never outboxed in his career.