I finished both of these builds about a month ago.
I built the underfolder on a fixed stock Vulcan receiver (I think it was Vulcan centerfire had them a while ago for like $30). I had do a lot of work with the dremel to cut out the underfolder holes after using the drill press. I just oxphoblued the rivets and left the receiver the way it came, it's a pretty good match. US parts used: receiver, FCG, pistol grip and slant brake.
Pistol started as Romy G, I can't take credit for the shortening process of the barrel and piston, but i did shorten the gas tube and cut and fit the lower handguard. I built it on a NDS-6 receiver as it comes marked from Nodak as a pistol above the serial number. The grip is a polish fat grip and put on a 4 prong flash hider for looks. I need to add the front handguard retainer and fit upper handguard wood and refinish the whole thing.
Both have been test fired and ran perfect.