At #leaffest-2016, Molly DeBlanc and I followed the instructions and photos @stoft posted, which were really easy. @cfastie lent me some wood and it was simple to cut and sand 5 blocks and glue them together -- using some large drops of Elmer's Glue-All.
It took larger drops of glue and longer to dry than I'd guessed, but the hard part was actually putting it back in the card-paper enclosure once it was complete.
I left a tiny bit more space (2-3mm) at the ends of the wood block to make this easier, maybe a little more behind the wooden ramp to leave space for the USB cable, which I have knotted. I know this isn't an exact duplicate, but I wouldn't have been able to fit it in the box otherwise, and a few mm isn't the end of the world, right?
None, really, though I rubbed the bottom of the wood ramp to get the adhesive from the Velcro off, as I thought it might stop the Elmer's glue from sticking. Pretty easy.
Everything looks good, though I haven't yet glued on the slit -- a little hesitant as it'd be permanent, but no real reason not to; it could be cut out and replaced if need be.
I posted a question about reducing interior stray light, and will probably paint this with Sumi ink for a matte black interior.
I need to test it out now to compare to old data I've taken with the same device, though besides ambient light, it's really the same geometry and everything.
I'll need to do some endurance testing too, though:
More on testing soon. Feel free to use these photos in the original build instructions if they're helpful, esp. the ones showing it going into the housing.