NICE-looking Toy, ben77lemay!
Standard twist for the 7.62NATO is 1 turn in 12 inches; this accommodates the 145-grain military slug very well and also can do some great shooting with 150s, 165s and even 180s. Heavier than that and you will have to do a lot of praying.
ORIGINAL twist for Mauser 98s in the original 7.92x57 is given in Table IV, Page 250 of the TEXT BOOK OF SMALL ARMS - 1909 as 1 turn in 9.39 inches (1 turn in 240mm). This was regarded as suitable for the whole range of bullets from the early 227-grain RN to the 154-grain JS; it was kept when the JsS was adopted also.
Hope this helps, either now or with a future purchase.