The length of the rifle is going to be measured by the stock that's on it, not the length that the stock WOULD be if you had a different (i.e. pinned open) stock on the gun. The BATF doesn't distinguish between pinned open collapsible stocks, LE stocks with spacers, and A1 or A2 stocks when it comes to AR15s, they just measure the gun. Is it over minimum length? Yup, no problem, be on your way.
As far as the barrel nut, I don't know if that counts as a threaded barrel or not, I'm not that familiar with any BATF rulings about Norinco Uzis.
Of course, if you register it as an SBR you could get rid of that dorky lookin' 16 inch barrel AND have the stock anyway you wanted it. Personally I'm thinking of getting a post-ban Uzi (a friend of mine builds them from kits, using enough US parts, and reparkerizes them and everything) and hoping the AW ban goes away so I can stick the Uzi collapsible on it at 12:01 September 14, 2004.