I still don't know what the rifle was. Took some quick pics
Gew98 windage-adjustable backsight leaf
Going by the example that was offered here (a pity I forgot to save it before the auction closed:dunno:), the windage-adjustable sight leaf was attached as a direct replacement for the standard Gew 98-type leaf.
I played with the idea of getting it, for my "you never know when it will come in handy" drawer*, but lost interest when it went above 50 euros plus postage.
I think the scaling portion is a kind of wrap-round for the original base, which would therefore not have to be disturbed. Easy to fit, if you have a set and need it. And easy to swap back, for instance for original-sights-only competitions. Oh dear, now I am talking mysef into needing such an item! Next time I see one (if ever!) I shall have to check on that drawer again!
Patrick
*That's a polite way of describing a cellar crammed to the ceiling.