Here are some images that should help you identify some of the Turkish Mausers models. 

Gew.88 / 1903 / 1938

The Gew.88 is at the top and is readily distinguished by the single stack magazine extending below the stock. The rifle in the middle is a 1903 and has a clip loading slot that extends well above the receiver. The rifle on the bottom is a 1938, K.Kale, but would be hard to distinguish from a reworked Gew.98 except for the absence of K.Kale on the  receiver face.

The Gew.88 bolt on the left is identified by its tiny extractor. The bolt in the middle is a 1903 with its tear drop bolt handle. The bolt on the right is a 98 style bolt and would be hard to identify as 1938, Gew98 or even Kar98 without deciphering the markings.

Thanks to Mr. Ireland for these two pictures.