Pillar drill should be fine, Jem. You can put some coloured tape on the rod to mark the range of insertion depth you need.
Do test often!
Terry
I agree with Terry. The pillar drill should do the trick. The last one I did I was using the lathe to spin my flutes cleaning rod with sandpaper threaded through the slot in the rod. I didn’t need to mark the depth as I could see through the holes where the paper was. I started with 150 grit but found it was a bit slow so went down to 80grit, testing often - not just the note I was interested in but ALL notes up into the 3rd octave. Then when it got close to where I wanted the tuning I polished it successively with 150, 240, 400 grit. Could have gone finer but after the 400 grit it was more polished than the rest of the bore. Then oil.
Let us know the results.
Cheers
Graeme