Cool rifle, though a picture is worth a thousand words. If you can provide more pictures, we can help more. Good detailed pics are very helpful, particularly for things like barrel codes, etc. The extra effort to take apart the rifle can yield a lot more info.
Your rifle was built in Danzig in 1918, but rebuilt in the Republican/Weimar era. The 1920 denotes that it was in govt hands during the the weapon buyback program. Your rifle also has a blued bolt, another dead giveaway it was still in service in Weimar Germany.
The Kar98a was an evolutionary dead end so to speak and the Germans did not manufacturer more after WWI, and barely manufactured replacement parts. The ones remaining typically went to police units or other military units desperate for arms. Since new parts were not made typically, salvaged parts were used extensively. I have a "matching" rework 98a (also an 18 Danzig) that has salvaged parts renumbered at the depot level.
Look carefully all over the stock for any markings. Depot work is often recorded by a stamping on the stock (wrist, keel, some cases on the side of the stock (Cassel was famous for this) the stampings could be removed, worn, etc.. so lack of them does not mean it didn't go through a depot. Spandau, Cassel and Konigsburg were early depots, while Hannover, Magdeburg, and others were added later.
The unit marking, if imperial, I beleive is a signal battalion, but if it is Reichswehr or police (S.A. was used by police too--- Schutzpolitzei Aurich district-), I am not as up on those markings and their particulars.
Either way, a cool rifle and pleasure share more pics. A member much more knowledgeable than me may chime in if you do.
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