The 175 was the base model of the three A&D actions that Sauer offered. Your Model 8 was the second action, with the upper sear and Greener cross bolt, and finally the models 11 thru 18 which was the third, with intercepting sears, and Greener cross bolt.
The info and dating comes from Jim Cate's book on J.P.Sauer.

Best,
Craig