So the tapping went well
Lots of oil, and just wound it in, bars mounted on the bike, backing off a bit every half turn or so, and checking left/right up/down alignment regularly. The aluminium is surprising soft and easy to work with.
Bar ends fitted lovely!
I marked the positions for the switchgear holes, covered them in a few layers of sellotape, drilled a small pilot hole, followed by the actual drill size I wanted.
Again no problem at all, no slipping, don't know what I was worried about!
PS don't pick up the oily ally swarf with the Mrs' mini-Dyson. Looks like I may be buying a new one of those, Doh!