Any question answered...

Clerkenwell Screw is your answer, if you can't find it, get it tapped to M6.

You can, worse case scenario is that you may need to change the bottom bracket width to make it work better (it did with my 2x8)

Exactly, put it on.

Clerkenwell Screw is around the corner from my office, but I hoped not to have to go down and try every bolt of about the right size. Although they are very helpful.

re the BB, I assume you mean to move the front chainrings into a better line with the rear cassette - middle to middle as it were.

Cheers.