I just want to clarify this issue for those of you who may be confused. I have gone this route a couple of times now, so I am pretty well versed.
You must begin with a receiver that is either registered on the dealers books as a stripped lower or pistol lower. Carson Armory told me that Bushmaster told them that all BM lowers leave the factory booked as RIFLE lowers. That could make a difference.
I used a STAG lower and had my dealer do the 4473 as a pistol lower. I also got a copy of the 4473 so I wouldn't have to backtrack later if it ever came up.
Obviously, LV requires you to register it on a blue card. I am unfamiliar with that process, but you guys know what to do.
Once you have it in pistol configuration, you can legally add a 16+" barrel and stock (remember it must have 16+" or it becomes an SBR). This is legal thanks to the efforts of the great folks at TC Contender to get a ruling on the subject.
You CANNOT take a lower that has been been assembled and turn it into a pistol. Stupid, and it's the same thing as above, but it's the law.
That should cover all of the bases. This post is intended to help my brothas who may be contemplating this, but didn't quite get the gist of what was discussed in here.