Taking Louis' excellent analysis into account, I now wonder if your MS may not have left the Steyr factory until after WW2?

Perhaps it was assembled at or about 1939, 'pigeonholed' while wartime production (Under Hermann Goering) took precedence, and not sold until after the war. The 'double headed eagle' and even the 'KAL 6.5 NORM' may have been applied then?

I'm not finding any reference to that particular eagle proof on the 'net.

Again, I would defer to members Kuduae or Marblekonus for expertise.