Dave
Your idea has got me thinking. If I were to replace my diagonal with a more robust 2" model then put a Borg helical focusser attached to that, I wouldn't have any clearance issues. I'd need a new diagonal because my preset one already has problems with rotation under heavy loads and a helical focusser would push the lateral centre of gravity even further out when the eyepiece is pointing anything othet than straight up.
I've been thinking for a while whether it would be possible to motorise a Borg helical focusser, and I think there might be way.
I will investigate further.
  