Might not be what you want to hear, but just grab a Convoy UV S2+ (black body only, it seems, but about 10min to swap to a different color S2+ of your choice), and 20mm ZWB2 filter, and go crazy.

I still got a ’501 with ancient UV drop-in, probably 395nm, but no filter. You can pick up one of those for <10bux. For the price of the drop-in, might as well go whole hawg with the S2+.