Mayweather-Duran at 147 (Floyd-Judah version and Duran-Leonard I version) would be a classic fight. It'd be a SD/MD and a very close fight.
Mayweather was too small to beat Leonard or Hearns. Those guys were big WW's, I mean Leonard was big enough to fight Marvin Hagler at 160, can you imagine what Floyd would look like at 160???