Well, having procrastinated for weeks over the guitar re-wiring, I managed to get it done this evening.
It was actually much simpler than I thought, and I think I've learned a useful lesson about soldering - just start from scratch with new components! Clean new pots made soldering a doddle. I'm still not sure I've got the wiring right because I keep failing to update my drawings after I change things. I screw everything back together and then look at the drawings and suddenly panic. In particular, the wiring for the bridge pickup still baffles me, unless I've got the drawings wrong.
Nope, I've just checked - everything makes sense and the drawings are fine. Whew!
Tomorrow night I restring it and start setting up the action again, having tweaked the truss rod while the guitar was in pieces.