Kahlers & Fretless...

Crap! I look away for one day, and there's all this text for me to read!

JK!

Anyways. MadMike clearly has a handle on the dimension issues, and I will defer to his experience for that aspect.

As far as your question about balancing pickups, I believe it is true that if you are combining two pickups that are really different from one another, you will get one overpowering the other. But to be honest, I have next to no experience in blending a P and a J, since I have been running stereo for so long that if I have, I cannot recall what those results were. I do know that DiMarzio sell the Model P and J in a set, and have been doing so for several years, so I would imagine they compliment each other well.

As an aside, I once took a DiMarzio Model J, and split the coils up before mounting them into the stock P-style cases that came with my Yamaha BB300. I used these for my distortion channel for years with awesome results (my bass solo video/recording was done while playing this exact bass and combination). I've loved DiMarzio bass pickups as long as I've loved Kahler bass trems.

Its funny, never thought I'd be a P + J guy. The Willpower on my Attitude has always and does still sound amazing but with the Fender Fretless, the P + J sound great together with overdrive and even the J solo'd does aswell. The J pick is a custom one for the Tony Franklin bass. If someone was parting one out I'd buy that pickup in a heart beat! I think its suppose to be based on a Dimarizo so maybe I will just go with the model J.