The Powermatic and Jet were the same machine, but the release of the "C" model under the Powermatic brand has changed things a little.
The 3520C has some improvements over the B:
Proper indexing
Magnetic, moveable remote controls. Relatively easy to retrofit these on the 3520B, see the Mustard Monster weebly
Closed legs
Tailstock quill with Acme thread (3520B is a "normal" thread - adequate, but not so strong)
Extended spindle nose for better access to the workpiece - the headstock block on the B sometimes gets in the way a bit (very minor issue)
Massively increased price!
Horrible mustard colour!
Duncan