Overall question is what to do with an already long in hand, put together watch and the degree to which it is,in fact, put together. OP has decided to service and wear.
I dont think there is anything wrong with the case or case back, just the wrong bezel ? Experts please chime in !
The markings on the inside of the case are consistent with the other online pictures I compared it to, the reference number on the back looks to be polished off !
It is a bit of a mess really. I have serious doubts that it would ever make a worthwhile project as it seems to be a bundle of questionable bits banged together. - Case is late 50s possibly 60s but will need serial and reference to identify it correctly. Caseback corresponds. However, difficult to make out. Seems both are well polished as edges are round. I would expect a tachy bezel with that case or a different dial if that is the bezel belonging to the case. - Hands are not right for case or dial. They are a bit of a mess with H, M and S being some sort of non UG adapted look alikes. Second runner looks wrong. - Register hands look the part but i am not convinced. There has never been a red register hand duplex in the UG line. - Dial is a 60 tri compax moon dial with missing lume. It also shows fading at arounf four o clock so likely it was cleaned up. - Movement shows corrosion . It may be working but for how long ... That leaves what, the crown ? Cant see much of it but probably work breaking and selling as it is never going to be a 20K watch without some major major parts sourcing and specialist work. it could be better and I have tried a middle of the road assessment with what I have (low res images) which is not that much.