I don't think I am mistaken, but weren't original Mauser sporters built by Mauser with the dovetail slot scope mount?
Pretty sure that is the case.
I can't imagine such a rifle being refused for proofing.

Why would a rifle need to be reproofed other than in the instance of a rechamber or rebarrel? Do some European countries require re-proof after a certain period of time or just when a gun is modified from its previously proofed form?