This is a 41-42 that is LuftAmt proofed.  Most of these guns have a Ku either before or after the serial number.   This one does not but has all the characteristics of the Kus.  It is in the correct serial number range, has one "42" armorer replacement part (the side plate) and the rear toggle link is not numbered.  The barrel and grips are E/655 stamped.