After discussion with Rahul, I've made the following additional changes to the GeNS system:
0.5'' Lens Mount
Hemisphere Mount and clamp
The total height reduction I found was only 0.25'' total, which is quite small. Because I have considered the top of the periscope mount a constraint on the location of the bottom of the sphere base, and because the lens mount does need some height to function properly, I don't think I can squeeze much more from this stone--perhaps the sphere base could be a bit thinner, perhaps we could use a different periscope mirror that requires less vertical room, if we never used the 0.5'' lens mount and only used the hemisphere clamp it would save a bit, and finally we could reduce the height of the schwarzschild though not by much. The cost of this 0.25'' is the need to machine a new hemisphere mount and clamp, holder posts, and base posts.
See it on the DCC: