Neil,
I would agree that a stair opening in the South makes sense if you do offset your pier to the North. That's what I did, and the pier ended up roughly in the centre of the 'circle' left after the floor cutout, which was 600 mm wide by 92 deg of arc, was made.
When I had the LX90 mounted on the pier, it was alt/az. Refer to several of the pics on my construction thread.
http://www.iceinspace.com.au/forum/a...9&d=1273837479
With my current GEM, there is a surprisingly large horizontal offset between the OTA axis and the pier. As I think I said in an earlier post, when the scope is pointing North, I'm guessing that it would be 600 mm or more offset from the pier centre line. Hence the dome slot needs to be considerably 'off' North to line up with the scope.
Cheers,
Chris