Turntable is 33", I want to be able to turn a Y6b or Allegheny around without issue.
The top three spurs were meant to be industrial tracks (my choice of color to differentiate industries from yards could have been better!). To avoid taking consists off the tracks I would like to build a storage layer (not yet designed) and have everything able to run between layers without having to be removed from the track. The reason I don't have the switches running along the long section is that I want to reserve that swath of space for mountain scenery, but again, everything is subject to suggestion and change!
I am tinkering in SCARM again looking at 6" offsets for curves like gunrunnerjohn suggested and am revisitng how I have the whole layout structured including where industries and their switches are located. I really want the 4" offsets to work, but since I have time, I may as well work on an alternate plan that takes this good advice into account 
