Is there any videos on that process?those are exactly the same as AKS-74 trunnions. not that you would find these readily either. but AKS-74 trunnion in turn is 99% identical to regular AK-74 trunnion. Find yourself an AK-74 bulgy kit and you are all set for your AKS-74U build. you can drill latch pin hole and make it into AKS/U trunnion in like 5 minutes time.
once you have your sidefolder receiver, you push-in front trunnion into it, line up with rails and/or front edge - final location where trunnion going to be riveted in. once it's lined up just use transfer punch or a dill bit to mark location of the trunnion hole using pre-existing corresponding hole that's already in the receiver. then take out the trunnion and drill the hole. it'll be metric so you will need a set of metric bits. i think hole is either 3, 3.5 or 4 mm. can't remember now, but you can easily measure a pin shank diameter that goes into the hole. note of caution: hole in the receiver will be larger than hole in the trunnion. receiver hole is sized to accommodate flange just below the pin head, trunnion hole is sized for pin's thinnest body portion.