It's going to be on the volume.
We discussed some options, whether we did a Jazz style V/V/T and use the Volume or using a V/4W/T...And I just favor the tonal flexibility of the 4 way as well as the fact that I think it sounds better than some of the weirdness you get with V/V/T where you have to unbalance the pickup volumes a little to get the low end to open up right.
I believe that this allows the shop to use the tone circuit they currently use on the SP without much difficulty. I've asked for the 'push' (in) position to be series and the pull to be parallel. I'll most likely use the series setting more often and it would balance better with a traditionally wired P-Bass split pickup tone which is series as well.
My other thought had been if I'd gone V/V/T I could have pushed my luck and had S/P push pulls on BOTH the volumes for each of the pickups, which would be pretty close to 'full Dingwall electronics kit'...but decided not to push too much or rock the boat that hard.

They're already being super cool about doing this much for me. And again, I really don't favor the Jazz Bass control layout anyway.
...Though I'll consider this bass to be a Super P-P,since it won't have much of a much that's anything like a Jazz Bass anything on it. It really ends up being a 'double P'.