I got there in the end!
This took a while to really get right. I knocked the parts together pretty quickly, but didn't really gel with the instrument. I bought a maple neck, and I've swapped this between the Jazz here and two P Bass bodies I have (one white and one sunburst).
The bass above is the Jazz body I bought for this project and a MIM Jaguar Bass neck I already owned. Its a Jazz neck with a Jag decal. I went with the 500k pots and Dimarzio Area J pickups. The cap is quite a high value, maybe 64 nF or something like that? I have a wee bag of red caps I pulled out a dead EQ pedal and I used a bigger value cap than the usual 47 nF as I wanted a dubby tone where necessary. The control plate and knobs are made by Hosco and the bridge is a Fender Badass II style unit.
I had some fun choosing a pickguard. The red tortoiseshell example here is a £8 'Floer' pickguard from Amazon. I widened the bevel on it to 30 degrees to match a vintage Fender, then wet sanded the edges. Finally I wet sanded the whole guard with 3000 grit, then used a rotary polisher to make it glossy again. This sort of melts the edges and screw holes slightly which makes the pickguard look a lot nicer.
Oddly enough the bridge is slightly off to the right. Fender pre-drill the body for the bridge, and add some guide holes for the control plate and pickguard. This seems ass-backwards as pickguards are usually a universal fit, whereas bridges can be a bit irregular. The Fender Badass bridge is also pre-slotted for quite a tight string spacing which is a bit unusual.
I bought the white P Bass body last month and had to drill my own bridge holes using a straight edge and maths. Not sure why Fender got it slightly wrong on the Jazz body as I did a better job at home as a DIY effort. It isn't a deal breaker on the Jazz bass, but a bit annoying.
Also annoying is aftermarket Fender necks. They are pre-drilled for the Fender tuners used on MIM basses. You either have to pay too much for an OEM set, a Hipshot set designed to fit the MIM screw pattern, or find a set of used MIM tuners. A few months back I sold two sets of "spare" MIM tuners only to realise I needed a set again! Cue another trip to Ebay.
I've got the screwdriver bug now, so I plan to keep chopping and changing. The white P Bass body is getting a fretless MIM Jazz neck. Somebody was selling one on Ebay for less than the retailers have them listed for, so I snapped it up.
The maple Jazz neck is now going on the sunburst P Bass body. This is getting routed out for a Toaster-style neck pickup and extra volume control. It will be something like Stu Cook's modified P Bass. I'm hoping I can get some of the tones of my 4003 from this bass once it is complete.