I did a little experiment looking at camera spacing, so I made a single side. This allowed experiments with lens spacing via the mounting bolt through slots in the grey plastic plate. The ledge provides the registration for alignment.
All the pieces are coming together. I whipped up a frame with proper angles and a bit more rigid than cardboard out of some PVC sheet. I had a great time making jigs and cutting everything out in my shop at home. Mostly table saw with a crosscut sled and some precisely angled blocks and a router attachment for my Dremel. All glued together with PVC cement. The slots on the top allow access to attach and tighten the nuts on the back of the camera mounting slots. There’s a hold in the base under the top camera mounting hole.
The camera on top is located such that the lens is at the centre of the pentagon. We’ll see what sort of gaps that leaves in the ceiling. The whole thing sits on an old IV stand