I've discussed this one quite a bit, my opinion is that Napoles would Decision him due to his better outside boxing ability, though Gavilan was very versatile in his own right.
Therein lies the problem any time Napoles is brought up in a fantasy matchup, anyone can justify their choice by claiming a cuts stoppage. Not saying that's what you're doing though, as this fight is pretty even. I see it being a very technical affair with plenty of versatility involved in the boxing and exchanging, but I don't know if Gavilan would be the one to cut him, even though his punches were quite unorthodox, sharp, and thrown from all angles. He just didn't have the power to hurt Napoles IMO, and though Napoles was a big puncher himself, Gavilan's jaw was iron. The edge I give is to Napoles's outside boxing and defense, though Gavilan's defense was good as well. That's why I'd favor him to take the close Decision.
I've actually always seen this fight going this way. I feel that in a mostly evenly matched, tactical battle, Napoles will be in control more often then not due to his better work on the outside. Power isn't going to come into play here because Gavilan wasn't a puncher and Napoles won't be able to hurt Gavilan. Napoles superior footwork and his edge in defense earns him a close but clear decision in a chess match. Of course there are chances of Napoles cutting here, especially considering Gavilan's fast, sharp punches, but I don't see a cut forming in this fight on Napoles that will be bad enough to stop it. Napoles W15 Gavilan, probably 9-6 type decision.
I discussed this one recently aswell, I do pick Napoles, i think he could offset some of Gavilan's aggression with the subtle footwork, and in a boxing match i think he would have a slight edge. They will fight at times, and i may give either man an advantage there, maybe Gavilan though as he was a relentless combo hitter at times. Imo Gavilan's big chance would be to outwork Napoles relentlessly, anyway, i pick Napoles to do a bit of what he has to over the stretch, get the combos in and slip out of range just enough to get the decision.
Just to be clear. I'd favor Gavilan by decision with a possible stoppage on cuts. These are two great fighters and I don't think you could go wrong either way. It's all perspective and I'm looking at the pre 50's Gavilan who beat Ike Williams a couple times and gave Robinson fits. I rate Gavilan's boxing ability pretty high. He wasn't as smooth and versatile as Napoles, but what he did, he did good. Napoles has a very good win against Griffith, but I don't place any of his other victims in Gavilan's class. I don't read too much in to Napoles loss to Monzon, but I do think Gavilan's height doesn't hurt his cause. Gavilan has a lot of impressive wins (albeit a nearly equal amount of "quality" losses). Just my perspective. I don't think it's a slam dunk either way.
Slight edge to Gavilan, by decision, though could definitely go either way. I hold both fighters in very high esteem indeed.