WAIT on removing the sideplate rivet! Later ones were removed by the East Germans - and I am sure some in the USA because of lost sideplates etc. Once off, that rivet is harder to replace than leaving it alone
Here is a 1939 - S/42 (Mauser) police
pictures show the gun with the original cut sideplate and then the next two show a non-cut sideplate and how it won't sit properly
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Two pictures of original cut sideplate for police sear safety - note, further information is in the FAQ in New Collectors stickies