I've only heard raves about the J99 pickups barring the single coil hum that you'd get with any other true single coil pickup when solo'd. But if you do go with a pickup swap, I think both neck and bridge J99s are the same size so keep that in mind.
On my Carvin they are the same size. If |I get a chance, I'll come back w/edit and tell you if the both of them match the Jazz'es neck or bridge PuP.