This is my initial concept , on the rough template;

P-Bass and J-bass pickups, '51 P-bass control plate and concentric pots.
But now, I'm warming to the idea of this neck pickup and this beast near the bridge, with 4 knobs, like a Toronado guitar.
Either way, I've already cut out the body from ash.

It's a bit on the thick side, like 2 inches bang on.
I've started on contours to get around this.
I'm thinking of adding a scooped section where the neck plate is, so I can use standard length neck screws.
I have the neck, a Squier Bronco Bass item, that I tinted with french polish and laquered with clear nirtocellulose.