Possible found a clue in Mauser Military Rifles of the World 4th edition page 66 of the section concerning Brazilian models. Briefly mentioned at the bottom of the page is a DWM 1898 long rifle with commercial markings and proofs similar to the rifle in question.
Very good match! I think that must be it!
Last edited by Patrick Chadwick; 01-13-2016 at 07:23 AM.