The buttplate is from a Mannlicher-Schoenauer 1903, I've installed a few on custom stocks over the years. I used to be able to find them in boxes of miscellaneous parts at gun shows, but that source has seemingly dried up lately. Google pictures of Adolph stocks, he used them pretty often, even had them engraved.
To me, that rear sight looks like it was installed on a contoured ring that was left when the issue barrel was turned down. The chamber bulge diameter in front of the ring is quite a bit smaller, compared to the action diameter, than the issue barrel would have been. Maybe I'm wrong, but my thought is the quality of the work done on that gun doesn't equal the use of a clip on sight.
