AK-47 would have the been the primary small arm by the late 1950s but there would have been significant numbers of SKS carbines still in service. From the point of view of doing a conversion that makes for an easier transition from a WW2 Soviet figure as the basic uniform and equipment is near identical just meaning you need to convert the rifle, which, whilst a fiddly task will be a lot easier than trying to convert a bolt action rifle to a pistol gripped AK-47.
RPDs were the main LMG but no doubt there were still significant examples of the lesser known RP-46 floating around, which again offers easier conversion options. Basically you remove the drum magazine from a DP and add a belt.