I don't want to rain on your parade, but I believe the reason there are no British or other proof marks, visible on the barrel (at least), is that the rifle looks to have been refinished, and possibly after a new barrel was fitted? The reason I suggest this is, the number stamps used for the serial number on the barrel, are of a different style/font, from the action serial numbers. If it was original, I would have thought these would have been the same style/font? This is just an observation.
Now please consider that I am no expert of Mauser firearms and espacially different or unusual types/models, so what I have written above, may be all BS.
Regards Homer
-------------------- "Beware the Lolly Pop of Mediocrity,
Lick it Once and You Will Suck Forever"