I have one very similar to the OP's, had her for years and have not seen another.
Mine is a DWM made South African military property stamped (Arrow inside a U on top of receiver and in the wood on top of grip) 6.5x58mm M1904 Mauser-Vergueiro.
It is stamped 15 MR over 2 over M just above the crowned CR stamp on the right side of the stock, it has 93/373 stamped in the butt heal just behind the rear sling swivel as well and has UDF 15664 stamped on top of steel butt plate and NP 6.5mm 2-11" 37 GRS NC. 155 GRS on the barrel.
The bore is like new and bluing bright and is 90%, also it is all matching with cleaning rod except for the Bolt sleeve and safety which both match themselves. Bolt has the correct serial number. Bolt is in the white and is shiny like chrome.
This bolt is super smooth in operation, it almost opens and closes by itself with zero side to side slop.
This is what Smellie had to say about it -
"When Portugal sent the Portuguese Brigade (actually a Battalion) to fight on the Western front in the Great War, the Germans refused to sell them any more ammo: no sense of humour! So the logical thing happened: the Portuguese traded their Vergueiros for SMLEs and the Brits supplied them with ammo... and tin hats.... and Vickers guns...... and Lewis Guns and so forth. Portugal was very much a poor country and lacked just about everything for a modern war..... but they were willing enough to FIGHT a Britain's OLDEST ally: BEFORE the Armada.
The now-British Vergueiros were London proofed and sent to South Africa, closer to a steady supply of ammunition, especially when von Lettow-Vorbeck invaded Portuguese East after the Battle of the Bees at Tanga and the ensuing invasion of German territory by the South Arican military (with strong British backing). More Portuguse rifles would have followed when Portugal upped its single Battalion TO a Brigade, which was called the Portuguese Division.
Much fighting between SA/British/Portuguese troops and German troops ensued inside Portuguese East. When the Germans were chased out, they did the logical thing... and invaded Rhodesia! World War One actually ended, in the field, in November 25, 1918, when the Kaiserliche Schutztuppe assembled on parade in Abercorn, Rhodesia and formally surrendered their weapons. At that time, the German Army in Africa was armed largely with Lee-Enfields.
The Kaiserliche Schutztruppe's Askaris, their Black soldiers, finally received their pay in 1964, shortly after their great leader's death. He had lobbied for many years for the owed back-pay for his army.
Your rifle is Portuguese, made in Germany, and has London proofs with South African unit markings from one of their Mounted regiments of Rifles. There are at least 3 like it in Canada, of which I have seen 1 but own none. I did a piece on the first of the other rifles in the NFA Journal in 1979, so it's in there.
you have a real chunk of History there, friend. Treasure it!
Hope this helps."