Well Dons, as you have Jon Speed's first book,"Original Oberndorf...", go to page 146-147 "Marking for Export"for the position of the Mauser # only on the bottom of the receiver. Continue with page 150 "The Mauserless Mausers" for the lack of the company name. Then page 162: the Mauser banner was only stamped on actions since 1924, but we are around 1900.
On this action, we have two sets of serial numbers: The Mauser # 1125 points to the action date 1899, see page 433. Then we have a Sauer & Sohn serial number 89057. According to Jim Cate's book "J.P.Sauer&Sohn" this S&S # points to 1903-4. Okay, in the photos the Mauser serial # on the rear magazine wall is illegible, but there is a "Blur" visible in the correct position, right under the receiver.Smaller trigger parts still show the end #25. The Suhl people apparently tore the actions they had to "buy in" from Mauser (no other action maker, as patents were still valid)down to parts, modified them and assembled them into their own, distinctively shaped rifles with little regard to the Mauser serial numbers. On the "W.Foerster" rifle mentioned above, top and bottom metal have different Mauser serial numbers, but as they are engraved by the same hand they were probably assembled this way before 1912.
For the shape of the triggerguard and early double set triggers, go to page 427 and look at photos #969 and 970. IMHO this action is the complete commercial Mauser transition action #1125, made some years later by Sauer&Sohn,Suhl into a sporting rifle and in parts renumbered by S&S in visible places into their own range, #89057.