The mirrorbox cross section shows how the mirrorbox walls are cut away halfway down the height, so that the octagonal secondary cage precisely slides in. Also visible is the side view cross section of the 6 point mirror cell. On top of the mirror aperture stop there is room for a 4mm thick dust cover. Also visible are the aluminium L profiles, and the corner supports in the top of the box. These corner supports carry the T-nuts that hold the screws fastening the trusses.
The center of rotation is exactly in the center of the top of the side walls, naturally coinciding with the center of the alt bearing. This should also be the scopes' center of mass. If not, the room in the corners of the mirrobox can be used for counter weights. Alternatively the counterweight may be implemented with a pull-spring.
NOTE: Although the figure doesn't show, the collimation bolts are supposed to be spring loaded.