Hi guys, sorry to bring an thread back into the light but I just found out what the double s mark is for, These are the replies I got from the members at gunboards:

First one, Hi, looks like the Swedish inspector mark of Sten Stenmo. In 1939/1940 Sweden bought 5.000 K98K from Germany. They converted those rifles to fire the powerfull 8x63 m/32 machine gun cartridge. This type of rifle is called m/40 and very hard to find in it's original configuration.

In 1948 Sweden sold the m/40 to Israel. There they were converted to 7.62mm during the 50's. Besides the inspector marks there is no difference compared to a standard ex-German Isreal K98k. The few examples reported are produced in 1940, codes are 147 and 243. There are more but I dont want to make this boring