Leonard should be able to handle him easily. Leonard started at 147 and made his way up to LHW. Same thing with Tommy Hearns. Those 2 guys started as large welterweights ( especially Hearns) and became champs up 4 weight classes, similar to Mayweather's ascension from 130 up to WW/JMW.
The H2H matchups with Floyd & Manny against the Fab 4 aren't ideal due to their natural/ideal sizes. Except Duran, that's fair. Floyd would be a tough matchup for anyone from 130-140.
That's honestly how I feel about him from a historical perspective as well. I truly believe he would've been successful in any era, but he would've fought exclusively between 126 (was a 125 FW AM) up to 140 lbs (when the JWW division was in existence.) I don't think he would've made any attempt at going up to 147 lbs in many different eras- when guys like Leonard and Hearns were ruling the division all the way back to guys like SRR, Burley, even a bit later guys like Emile Griffith. These were really large 147 lbers. Out of the fab 5, the only guys that were close to him size wise were Duran and Benitez. But I think he's competitive with pretty much everyone from SFW to JWW. He was really a complete fighter by the time he made his way up to 140 lbs.