Well, at long, long last all the parts finally came in to replace the ones that were cut out of tolerance. I welded the viewer screens together using my custom jig.
I had to cut a shelf into the cast part, but otherwise it fits very well.
(I'm holding it at a bad angle here, but that back part does sit flush with the black cast piece.)
Added the radii using my router table. (Sorry, forgot to take a photo of this step.)
Then body filler to smooth over the steps (laser cut acrylic isn't super precise, especially at different thicknesses).
Today I sanded and primed, better to see the spots I have to go over again with filler tomorrow.