As stated, do not place a folding stock on the weapon as it will be a violation of USC 922(v) - assault weapons ban. As I understand it (99.9 % sure here), you can place a detachable stock on the weapon (922(v) forbids folding stocks, but not detachable stocks)), *BUT* it must have a barrel long enough so as to ensure that the Uzi type rifle does not fall under 26 inches with the stock removed (illegal short barrel rifle). Since it is a detachable stock, the Uzi type rifle will be measured from the front of the barrel to the rear of the receiver (EVEN IF THE DETACHABLE STOCK IS MOUNTED). Don't get caught with a detachable stock on your weapon with a 16 inch barrel. You may be able to get away with this if you buy an 18 inch barrel from Quality Parts?? Call Bushmaster/Quality Parts and ask about this. I went with a folding stock - it fits this weapon fine. My brother mig welded the stock open and I repainted it (refer to pic) .
When I removed the thumbhole stock and placed the separate pistol grips and stock on the rifle, I found there was "play" between the pistol grip lower and the receiver (when you remove the thumbhole stock, this may become apparent). I used a pair of plyers to bend the tab on the pistol grip that inserts into the receiver. By bending the tab downwards, the receiver and the lower pistol grip become completely solid.
Here's what I did to comply with 922(r) : (1) I added a Quality Parts (Bushmaster) chromed barrel, (2) Group Industries pistol grip (D and D Sales), (3) Group Industries forearm (D and D Sales), (4) operating rod/recoil spring (D and D Sales), and (5) promag floorplate (or you could make your own floorplate). Before you ask, D and D Sales does not have USA Made triggers or sears.
I have an original letter from the Firearms Technology Branch signed by Ed Owen that states the Uzi Type Firearm has 15 imported parts on the rifle. My letter states that there is no hammer on the Uzi rifle. I know there is another letter out there that says the Uzi rifle possesses the hammer, but I'm going by my original letter.
Stay away from using USA Made Magazines. I've tweaked my Promag mags and could never get them to work reliably. The Promags work OK, but they weren't reliable enough for me. This is why I use the floorplates (slightly modified) to work on my IMI, South African, and Argentine Mags (I had bought 5 promags cheap at a gunshow). For another USA Made part, you could make your own wood stock. It would be simple with some basic tools.
I really liked my Norinco 320 (I sold it and now have a Vector subgun) and I've had fun working on it. It was 100% reliable. If you like to tinker, this is a fun gun.
Dan