Advice on an Oyster Lipton?

[e2b]

Looking into an oyster lipton for a friend of mine, was in his family. I'm somewhat familiar with Cal 59 watches, however this one has me a bit puzzled.

Keeps time, movement seems good, case has some plating issues (but it's an old watch and well worn).

After doing a bunch of research, can't figure out what's going on with the case back and wondering if anyone has any advice? It's got male threads coming out of it, so needs a female threaded back, the original back is missing. Has a "I.D. Case Co / Wherever / Sportsman" case back on it.

Also looks like the crown tube was machined down and a generic crown was fit. Crystal is a super high dome, and shaped like a bubbleback crystal.

Any advice would be much appreciated! Also any sources for parts for these watches would be much appreciated!