After just a little sanding on both the OD of the lux meter cylinder and the ID of the acrylic cylinder:
Next, mark the acrylic cylinder for the wiring hole and drill it. Then put it together:
The hardest part was getting the tiny screw that holds the diode plate in place without hitting the electric cable behind it. I used needlenose pliers to put a kink in the cable to clear the mounting screw.
Finally, I got the lid back on top of the lux meter cylinder:
Somewhere along the way I put a hairline crack in the filter that fits in the lid, above the diode. I'm assuming that will have negligible effect on the operation.
To hold the lux meter cylinder in place, 4 small drops of Weldon #16.