I don't have a proper answer for you, but my last can came with a muzzle brake and a few other parts and tools. I had some discussion with one employee as to weather or not it was mine yet. I told him of course it was, its paid for and therefore mine, I just can't take possession of it yet. I ended up leaving the store with everything but the suppressor itself.
I wonder with the rifle if the LGS may site some warranty issue with separating the halves. Makes since to me that you should be able to take it home as you could just as well go home and buy a pistol upper and have it shipped right to your door. However I really don't know what the ATF has to say about it, most likely they don't either.