When I converted my Pro IV to passive, I tried wiring it with two volume, two tone. I used the wiring from a stack-knob J as a guide and it didn't work very well for some reason. Maybe my allergy to J-basses just made that a preordained failure. Then I wired it VVT, with a selector switch in the fourth hole. I'm not happy with that, either but haven't rewired it again. The bass is already fretless, and I'm considering getting it refinished. If that happens, it will lose a couple of the holes and become VV only with the other two holes blanked off and filled.
Now to figure out what color a fretless Thunderbird with Alumitones should be... It would have to be a non-traditional color of some kind, but that might take a while to decide. It always does. I'm currently thinking it should be 1968 GM Rallye Green. That would be different from most Thunderbirds, with the exception of one of Veronica's green 'Birds.