B-Diddy is one of the greatest UCLA Bruins ever ... and tells TMZ Sports the former Suns head coach and ex-UCLA player is the right man to replace Steve Alford in Westwood.

In fact, Baron wants to see Earl coach the team so badly ... he says he'd be down to be on Watson's staff -- and UCLA wouldn't even have to pay him!!

"If Earl Watson was the head coach, I would coach for free. I would do whatever for free."

Of course, lots of ex-UCLA players agree with Baron ... guys like Matt Barnes and Lonzo Ball have already made it clear Earl would be their choice for the job too.