Proper way to shim lens mount?

I recently disassembled an Edixa SLR to reglue a shutter strap that came loose. This required removing the mirror box and consequentially the lens mount from the camera body. The mount had a number of shims behind it to align it properly with the film plane. I want to know what the proper procedure is for checking the alignment of the mount with the film plane. I assume this is something that cannot be done by simply checking focus at the film plane with piece of ground glass, or can it? I doubt one could see a tiny amount of misalignment this way.

I think the hardest problem would be to get the film plane exactly even with the focus plane of the lens. It is going to require some sort of complicated rig in order to deal with this problem.