TT;
I have one of these guns SN 87,934. Mine too has the 70 stamped in the extractor face for the 2 3/4" chambers. I paid considerably less for mine, BUT, the entire forend assembly was missing. Mine also had a raised cheek piece which is leather covered. The leather is torn & partly loose. Beneath it is what appears to be a slab of cork inlet into the comb & covered with the leather. Although the plates have the general appearence of a bar action, it is indeed a back action lockwork. I was rather impressed by the sear design. The sear mounts vertically with the lower leg being pushed forward by the front surface of the trigger blade. The upper leg has the sear on its end engaging the hammer on its outer periphery @ maximum possible distance from its pin. The sear pivot is thus very near centrally located & while it does not have intercepting sears it would seem from its design to be highly resistant to a jar off. Considering the condition you state for your gun I would think it most likely you got a lot of gun for your money.
The 2 3/4" shell was I think quite popular for both Waterfowl & Trap guns. Considering the weights of both yours & mine being 7½lbs + I am not at all surprized at the 2 3/4" chambers. I have seen these Sauer/VL&D guns advertized in a "Game Gun" wt of around 6½lbs. Don't recall if chamber length was stated or not, but quite possibly they may have been 2 5/8"