Texgunner, if you pulled the forend and barrels and made a clear photo of the water table and bottoms of the tubes you should get some proofmarks and other coding that a Germanic gun expert can identify (I'm NOT one!).
The best place I've found is the German/Austrian gun forum on the website
www.doublegunshop.com/BBS, but you can also ask on the general doublegun forum (the first one on the site). Some serious experts hang out both places and it is, in general, a very civil website.
Hard to tell where a drilling was made and by whom, since many of them had the major components sourced in the white from big old factories like J.P.Sauer and Sons, or Simpson Suhl, or Kreighoff, and finished by a smaller gunsmith or small factory and then often marked by the shop that sold them.
So it gets complicated. But an expert can usually tell you at least where the larger components were made (and when) and what country the gun was intended to be used in--where the final proof was done. And some guns just remain mysteries, even to an expert.
What a nice "mystery" to to try to solve!