The epi(dia)scope option is certainly something to be followed up. I have trouble finding lens sections of the lenses, though. It clearly isn't a Leitz...

The problem is that the lens mount of the unit I have in hand does not have a focusing helicoid, which is required to focus the projected image (as a student in the 1970s I used these monster devices to project pages from books for discussion in tutorial presentations). It looks more like a fixed focus unit.
And all cinema projection lenses (which would have a fixed projector to screen distance once installed) I can find are smaller..

Also, all projection lenses I have seen, although exposed to the heat of the lamps, don't have these weird holes...

I have been toying with the idea whether it could be an 'eye-piece' of a very large telescope, but all the cross-sections i can find there are also different...