I think it would be closer than people think...he was very fast at that weight and could hit pretty hard, and his technique was more fluid before he started aging. I wouldn't be surprised if Sweet Pea were to win but Shane would have a good shot.
Mosley at 135 was an amazing beast. He'd be more impressive at that weight than he ever was at 147+. Even with all that said, Pea would school him.
I think Whitaker would win a clear decisive decision, Mosley does not have the patience, footwork or Boxing brain to beat Whitaker.
I dont think anyone all time beats Whitaker from 135-140. ***with Benitez, Ortiz, Mayweather, DLH Armstrong giving him some trouble.