The photomicro L adapter is just a physical adapter, the optics provided by a separate projective eyepiece that sits inside the dovetail (parfocal direct projection isn't possible). As such all I needed was a tube with an internal diameter of 38mm on one end, and able to accept a standard thread (like m42) on the other end. As it turns out 1.5 inches is 38.1 mm, and 1.5 inches is a standard diameter for PVC pipe. As such it's easy to get an adapter with flat ends and an ID of 1.5 inches. It's also very easy to get a 38mm tube to m42 adapter since this size is used for leica and nikon photo tubes. I happened to have all those components handy.
So, all you need is a 1.5inch ID PVC adapter like this one (cost: around $2.50 or something), a 38mm to m42 adapter (around 20$), three set screws (~1$), an m42 spacer (~3 dollars) and an m42 helicoid (~16$), a bit of tape and the use of a drill. Total cost about 40 dollars, with potential room for cheaper substitutions.
The ID is a bit bigger than 38mm, so I put some strips of adhesive thermal printer paper until it could be press fit in firmly. That will hold it firmly but you can always retrieve the adapter later as well.
Drill three holes ~6mm from the bottom, and put the set screws in. I drilled them a bit small and put the set screws in by hand. A bit ugly, but functional. If you are more patient than me you could paint the PVC to match the color of the olympus scope and it might actually look pretty good too. The main reason I did not was painting PVC apparently requires some priming and long setting to be sure it's at maxiumum strength and I didn't want to wait before using it. I might make another one and swap the 38mm adapter over to it in the future.
Results are pretty positive.
(100% center crop)
Note that these photos were taken using a Nikon 2.5x projective eyepiece--this system was designed to use an Olympus NFK eyepiece, but they're more expensive. I'm honestly not 100% sure the NFK is the best choice anyway--it is a compensating eyepiece while the SZH uses non-compensating eyepieces, and I honestly doubt they add in abberations in the photo port to compensate. Either way the Nikon eyepiece does not seem to cause trouble.
Note that you could also just use this adapter here, but it doesn't come with a helicoid so it is still significantly mlre expensive than the DIY solution https://rover.ebay.com/rover/0/0/0?mpre ... 4215689212
You could also maybe get an mtv-5 without optics and swap out the c mount adapter for an m42 adapter, but that isn't a savings either.