I can only address your last question, originals were custom...if you wanted a scope the receiver was was modified to accept a non standardized claw mount. A shallow wide dovetail was cut in the receiver for the front (that was your windage adj) the rear mount were 2 screw holes the attach the female claw.
If irons were your preference, usually a two or three leaf was supplied.
I had a similar Sauer & Sohn, clearly marked 1927, in 9,3 x 62, claw mount, Zeiss Dialyt, well hunted with the scars to prove it, I had a hard time selling it for 750 in 2017.
I think the 9x57 calls for a .356 dia bullet. The 9x56 MS takes a .354 dia for sure.
Last edited by flintlocke; 04/06/24.