I bought another enlarger lens to do a sharpness test between lenses but wasn't about to drop $50 for a used lens board. With some CAD magic and a few drafts, I was able to come up with this. This lens board is for M39 lenses and includes a small piece to press fit or glue in that in theory should provide light to show the aperture setting of your lens (varies by filament settings and filament translucency). I have also sketched up a M39 jam wingnut with big ears to easily tighten or loosen your lens from the lens board.
Hopefully you don't have your enlarger exposing for minutes at a time but if you do, you may need to print this in PETG or ABS or PET-CF (if enlarger on for HOURS at a time). You should be able to get by with PLA but I have not tested that personally and have stuck to PETG.
The author marked this model as their own original creation.