I have to say that I disagree with your assessment of him vs. Floyd. No one dropped Floyd, so for you say Shane would've is off. Younger Floyd wouldn't have got caught like that and young Shane still didn't have defense, let's not forget that. Those punches Floyd got Shane with would've been worse at 135. Also at 135 Shane rarely outworkwd anyone, he out classed them, I can't see him out working Floyd, lol! Great fight regardless.
Now to answer your question: let's say Pac Man for starters. Go.
Zab dropped Floyd legit they didn't call it.
I think Shane would drop floyd, in his prime the hand speed, the physicallity, the pressure, and the power at 135 would have been Castillo on steroid imho.
The other thing is at 135 Floyd was prone to being more offensive, so it also gives you more opportunities than he gave you at 147. So it works both ways.
The punches Floyd got Shane with are what he got a shot and faded Shane with, not a prime shane at 135.
Shane's pressure and rate is literally what showed when he fought at his highest level, even against Vernon, Oscar, and Winky. He brought pressure, it wasnt till he got older that he couldn't bring it consistantly or when he wanted to and needed you to come to him.
Prime shane destroys Manny at lightweight, IMHO, same reason Freddie delayed the shane fight until Shane got even more shot than he was against Floyd.
What does Manny bring to the table against a prime Shane Mosley at 135? He doesn't have a great jab to keep him off, he was prone to getting touched, he doesn't have a hand speed or foot speed advantage. Shane has a better chin and I would say Shane has more raw power than Manny as well. I just don't see it being competitive and I see it either being a one sided beatdown similar to Moralles vs Manny 1 with a knockout in Shane's favor. The jab Shane had would freeze up Manny and Shane would be turning him never allowing him to set like he did when they actually did fight.
Just my 02 though.