@Jack P, did you use the Bachmann-supplied (cosmetic?) screw links, or sprung links such as Smiths'?
For anyone searching for these solutions in the future, and with apologies for the lousy 'phone photo, this is my attempt.
I used a burring tool on a Proxxon Micromot (Dremel-alike). With a little fiddling, and a fair deal of swearing, I was able to get the keeper nuts installed with a pair of needle-nosed tweezers. If I had a Markits screwdriver, though, I'd probably give that a whirl in the first instance.