You are close: it was a Spandau contracted receiver made in 1917, but built into a full Gewehr 98 at Danzig in 1918. Spandau ended rifle production in 1917, so the receivers they contracted from Pieper and Siemans & Halske ended up in Hannover, Dresden, Erfurt, Danzig, and WMO. The 1670 does not...