The WWII Czech Mausers are very interesting. One of the Mausers I have is a G24(t) DOU 42 all matching with the original sling and intact Eagle proofs. It was shipped back to the states in 1946.
The sling swivel marked "R" in from a Remington 1903A3, the rear sight patented in 1901 is the same one I have on my Winchester model 1906 22 caliber rifle. It may have been used on other guns too.