Drilling and tapping mausers with wonderful national crests on the receiver ring (i.e. Brazil, Peru, Colombia, etc.) has always been a painful decision.
I found a great side mount that lets you scope that mil-surp without drilling either receiver ring. You just have to remove a small amount of wood on the left side of the action wherein the plate for this mount is inserted and drilled and tapped into the action below the wood line.
This mount is quick detachable and returns unfailingly to zero when re installed.
It's the Griffin & Howe double lever side mount. Unfortunately this mount may not be fore everyone. The mount costs $400.00 uninstalled and Griffin & Howe charges $250.00 for installation on your favorite mil-surp, or any other rifle for that matter. Check out this link.
http://www.griffinhowe.com/mountsandpads.cfm If you want the more traditional top mounts and don't mind drilling into the crested receiver ring, then G&H makes custom two piece top mounts that cost $850.00 installed to your favorite mil-surp! Beautifully executed, even if they may not be for everyone.