Just to clarify, in CA we have the Year 2000 CA AWB which banned SALES (new or used, private or dealer) of any semi-auto centerfire rifle that can accept a detachable magazine and one of the following: Pistol Grip, Thumbhole stock, a Folding or Telescoping Stock, Grenade or Flare Launcher, Flash Suppressor, foward pistol grip.
HOWEVER, if you already owned the "assault weapon" and you registered it, you can do ANY "pre-ban" feature to the gun now that the Clinton AWB has died. You CAN NOT take a unregistered POST-BAN weapon (like a M1A) and make it into an "assault weapon" by installing a flash suppressor or a pistol grip stock UNLESS you, for some reason, registered it as an "assault weapon" before the cutoff date (01/2001 I think it was)
So the bottom line = The death of the Clinton AWB only allows us to modify our already existing and registered rifles to full Federal "pre-ban" (or "no-ban") configuration.
You guys in NY are lucky that you can still buy lowers as I'm sure there are plenty of people who would be willing to part with their decade plus old "pre-ban" AR lowers for a shiny new forged LMT/Colt/Bush/RRA/etc. lowers. If I lived in a "Free" state, I would be willing to part with my Colt Pre-Ban to a state that could take it (I forget which one ins't allowed to have Colts)