OK, well... having said I'd leave it alone, out of necessity I've had to revisit it fairly dramatically.
TL;DR version: neck developed what I can only assume was a truss rod fault of some sort, leaving me with action I could park a bus under and couldn't adjust. New neck bought from fleabay, turned up with a big DIY paddle headstock. After consulting the BC massive (see attached thread), the favourite shape seemed to be the old style Aria one as per this:
Anyway... just spent half an hour in the garage with jigsaw and 80 grit, and so far so good. Although that top curve has got a bit of a 'roman nose', now I look at it. Out with the 80 grit again then. Quite pleased so far though. A world of rubbing down still to come, and then the final finish is going to be the same as the original, i.e. white painted front to match the body, and the rest tung-oiled. I was really pleased with the oil finish on the first neck and I'd like to recreate it.