From Sean we received pictures of his MakerBeam mini-ITX case.
According to Sean the stock lengths of MakerBeam work for this exactly. The top and bottom panels he cut using something called the ‘shaper origin’ (a hand-held CNC-router).
He also used this tool to cut (and engrave) the plexiglass held by makerbeams. He was very pleased with how it turned out since it is hard to get the corners right. The plexiglass slots right in (<=3mm) but the corners need to be cut just a little to fit. The corner cubes do not have slots.
We agree with Sean. It looks great and is a job well done.