Thanks. I've never done precise drilling into a thick tube like this before, so all tips gratefully accepted.
I've also been doing some work on the repro grip = reaming out some of the wood so that the ring can move down enough to compress the nut against the grip. Geoff / bigduke6 very kindly added a spacer ring to it last year, but I've now discovered the nut is slightly too big to fit.
So my next interesting challenge is how to shave half a millimeter or so of metal off the outside of the nut without access to a lathe.