Keef, it's a 2" x 2" by 4" grey-painted Bud box, available from Mouser. I built the "One-Bottle Preamp" and its power supply in the same boxes.
One thing I like about that box is that it can be snap-together or screw-together. It includes a bag of four screws and a little tool to knock out the "snaps" and replace them with the screws, if you're so inclined.
This DIY can replaces two cans on a customer's unit: a single 80uF can and an 80/40/10 can. The mounting studs on the DIY can match the spacing of the twistlock base mounts on the old cans; so, except for having wires instead of terminals, it's a drop-in replacement.