Bridges is big and strong enough to guard a college 4. If he comes to UK, he will guard the 3 and 4 spots.
Offensively, it doesn't really matter as Cal doesn't emphasize positions. He can play Bridges at the 3 or 4 spot and still have him on the perimeter. It might be beneficial for him to play the 4 spot and force bigger, slower players to come out and guard him.
As for the NBA, the champs this year played a 6'7 Draymond Green at the 5 spot a lot this year, especially in the title series. They played a point and four perimeter guys.
Traditional positions are becoming a thing of the past, IMHO. They only really matter on defense.
At the very least, I think we should view players as Points, Wings, and Posts (or Bigs) more than PG, SG, SF, PF, and C.
Ulis is a pure Point.
Briscoe can play Point or Wing.
Mulder and Matthews are Wings.
Poythress can play Wing or Post.
Labissiere can play Wing or Post.
Lee is a Post.