I used to have a '72 Jazz Bass (that a friend of mine now has) that I modded in a few ways. I put a Rick hi-gain neck pickup in the neck/mid position of the bass along with a Schaller 3D bridge so I could adjust the string spacing a bit closer together to balance between the Rick pickup and the stock Jazz Bass bridge pickup. Then I rewired to controls with two volume controls (don't remember the values, probably 250KΩ
and added a toggle switch that I could select as a fixed tone control. The bass sounds awesome, still does in my friend's hands. 
