Hi folks!
Thanks for the replies so far.
Ou7shined - thanks for the suggestion. I had wondered about the V/V T/T combination, it could fit with what's left of the circuit, but I still have a nagging doubt that it wasn't what was there originally.
If I were fitting that from new, I'd have looked to 'pair' the controls physically, so that it was obviously either two sets of controls, (a V pair and a T pair) or (two sets of V/T pairs). If you look at the layout though, it's more like there's a single pot on it's own, a pair of pots, and a control that was almost on top of one of those pots. It just doesn't seem right that they'd put two pots so very close together given how they've spaced the other three - it'd be really hard to use one without disturbing the other next to it. A little toggle-switch though...
I'm still hopeful that someone that's had or has one of these will spot this and let me know for sure what's really missing.
Thanks again!