I reckon Gavilan is more or less the same size as Oscar, a solid 5'10 welterweight. He'd be at worst the second biggest man of Floyd's career, and Floyd didn't exactly do that well against the bigger boxing promoter.
Why? Oscar weighed in for 147 lb fights at 165, Gavilan weighed in at 147 on the same day, going to 150 or so for non-title fights.