Good reply, Wulfmann. I will just add that the magazine was altered from the original, which was a single column magazine that dropped below the stock. The notch in the receiver ring is to allow stripper clip loading of the 8x57, which is longer than the original 7.65x54.
Technically, it is a Turkish Model 38, but that is a sort of catchall term for all the older rifles that the Turks worked over in the 1930s to resemble the Czech VZ-24, the goal being to provide uniformity in appearance and training for their army.
An interesting rifle, but not a K.98k.
Jim