ive handled several parts kits the 3 that popped up ive seen over the years and also got to handle but not fire several bringbacks. all were made from Chinese k-50 ppsh smgs and retained the old chicom serial number below the front trunnion top rectangular rivet just 1 inch or 2 below the new shorter Vietnamese rebuild serial number. 1 had a black thick buffer in back that appeared to be homemade from an old military boot heal.
if you need any additional rare smg kit info just ask. I started very early as a young kid collecting everything and dealt in rare parts kits for about 20 years or since 1991 thereabouts. rare smg stuff always captured my attention.