P-bass neck to J-bass

Tim, Your bass necks should be interchangedable.  As long as your necks each require 4 bolts, you should be able to use either neck on either bass.  I've switched Tele necks with Strats, and I believe you can do the same with P-Bass and Jazz Bass models.  Good luck, Paul

I just tried putting a P bass neck from a MIM P bass on my American Deluxe Jazz bass.  The neck fits, but I couldn't adjust the intonation. If the open string was in tune, the bass was out of tune above the first fret.

The scale length is different, so the 12th fret on the P bass is not halfway between the nut and bridge on the Jazz bass.  So to make this work, you will need to move the bridge.