Yes; now I wonder what the head tube angle is.

is that 35mm x 1mm with RH threading AND LH threading (which would be Swiss and the LH would be on DS) or can you not determine what direction the threading is for the DS because the cup is brazed in place? if it turns out to be RH threading on both sides then this is French and so the frame is more likely French as well but not 100% certain since some Swiss (and some Belgian and Spanish, even the occasional Austrian) also used this standard but not nearly as many compared to FR. Have the framebuilder study the BB carefully and make sure it's really brazed in as well as what direction the thread is /was cut...SOMEtimes damaged threading was repaired by building up with bronze and re-cutting the threads...that 74 Campy spindle explains why the BB looks so weird, but not what the PO was thinking! Maybe he had some bizarre hip problem that a lopsided "Q-factor" compensated for...or he certainly could develop one if he rode the bike like that!

Well... i canīt test it, because it is damaged but by looking at it i would say its RH threading and LH threading. (Looks exayctly like the threadings in my Raleigh frame) Look yourself if you want.
This is the fixed side: FixedSide Picture (The brazed spot is not visible on this picture, itīs on the top, at 12o clock)
And the removable side: RemoveableSide Picture

Iīll try to measure the head tube angle now.

EDIT: Iīll let the framebuilder do that. Way too hard without the right tools. :-D
But: I did a comparsion with my raleigh sirocco and this old frame here seems to have a 2 degree higher head tube angle. (As far as i can tell by measuring with my eyball-protractor.)

sounds like and looks like this is French threading in the BB so more likely the bike's French too but again there were exceptions, It has no features that match with the major well-known FR brands (aside from the Nervex lugs and BB shell) so this is a rare bird. It still might help better sleuths to see the seat cluster/stay caps plus the dropouts/stay joints and the brake bridge...sometimes those details are good clues.

Lets see if these photos help. If not, I can make some more later.

Several months later: Still no Idea what kind of gem i got. Starting to give up to ever find out. It seems that iīm really going to make it a Noname Singlespeed, just to give it a use. If someone has a better idea or Parts please contact me or post here. thx!