You all have missed some details: The rifle is built on a commercial pre-WW1 Mauser, Oberndorf, action, evidenced by the large triggerguard with the set triggers built directly into, without a seperate set trigger housing. So there should be a Mauser commercial serial number stamped on the underside of the receiver ring and on the rear wall of the magazine. these would help to date the action more closely. Prior to WW1 there were no surplus M98 actions. The Mauser patents were still valid. Anyone wanting to build a M98 actioned rifle first had to buy in an action from Mauser. Before the great war Mauser sold more than two rhirds of their commercial production as actions or barreled actions to other gunmakers like Rigby, Holland&Holland, Sauer & Sohn and many lesser ones.
Another story is told by the proofmarks: The CROWN-crown/N proofmarks were in use up to 1912 only. They indicate proof by using the "4000at powder" made by Spandau arsenal for proof cartridges. This powder, loaded grain for grain, produced 4000 at instead of the 3200 at maximum sevice pressure when loaded in the 8x57I M88 service cartridge. As the deleted charge mark on the left of the receiver ring shows, the rifle was originally proofed for 2.5 gramm Gewehrblättchenpulver, the service charge of the 8x57I. Much later it was rebored, rerifled and rechambered to the 9.3x62, shown by the "new" 18.3gr bullet weight mark. The gun was reproooved with a 9.0 to 9.09 bore diameter (not groove or bullet)and for the 62mm case length as gun number 294 of October 1938 by the Zella-Mehlis proofhouse. As the old CROWN-crown/N marks were then out of use, but still valid, they did not bother to restamp new ones.
Prior to WW1 a "classic Mauser bolthandle" looked as "military" and "newfangled" as a AR15 clone looks today, so these were very often altered to this now unclassy spoonshape.