Install Face Plate
I got lucky with the acrylic face plate since it had a good fitting on the first trrry. This has an outer base that's recessed so the edges have a snug fit when it's pressed into the bottom half of the case. I have to install that first before the Raspberry Pi, otherwise it can't fit in.
Install Raspberry Pi
The Raspberry Pi rests on top of the four standoffs on the bottom half of the case. I inserted 4x M2.5 - 5mm machine screws from the top of the PCB until the head of the screw held everything in place. The screws need to be short or else it might not hold the PCB down very well. The holes in the standoffs are 2.2mm in diameter, smaller than M2.5 so that the threads can bite into the material.
Glue Top Plate
The acrylic window for the top half of the case did not have a tight fit. It's too loose and doesn't hold it's own weight, so I had to use some glue to secure the two parts together. I included some excess material along the corners. Put a dab of E6000 adhesive on the two corners and press them together.
Secure Top Plate
I let the glue dry for a few mutes before handling. I added a bit too much, but it was easy to peel off the excess. This is a silicone based adhesive, so it's soft. Definitely don't use super glue on acrylic.
Joining Two Halves
An inner lip protrudes from the top half of the case. This slides in between the walls of the bottom half. The tolerances are tight so the two are held together with just friction. I noticed the top bows slightly when it's joined with the bottom half, not sure if it the outer edge needs a bigger offset or if the material is slightly warped.