AW Ban:
Federally, any semi-auto rifle can have no more than two of the infamous 'evil features' (Detatchable Mag,Flashider,Pistol Grip,Collapsable/Folding Stock,Grenade Launcher,Bayo lug). In the case of collapsable stocks, from what I've read the ATF defines a legal non-collapsable collapsable-style stock as one that cannot be made to collapse without wrecking the stock. So if the pinning/gluing was done in a way that un-pinning & trying to remove the glue would wreck the stock, that's ok. Otherwise, no (from what I've read).
As for pistol/rifle issues, if it was a pistol first (i.e. assembled stockless, met weight requirements, etc) the fixed-stock can be removable WITHOUT being a NFA item as long as the barrel is >= 18in, and when assembled with the stock, it's the minimum overall rifle length. 'Registered pistol recievers' aren't NFA items, they're just regular AR recievers which the manufacturer builds into a pistol before selling (so that it can be either a pistol or full-size rifle, without worrying about SBR issues).
AOW status, IIRC, is for pistol SHOTGUNS only, a 'rifle caliber pistol' (like the 'Carbon 15 pistol', Contender, lone eagle, etc) is just a pistol.