This gun is one of the most common platforms that people use to unintentionally violate the 1934 National Firearms Act.
It is legally a pistol, and many people get the "bright" idea to put a paratrooper stock on it, since it will fit a Universal with a little fitting. Viola, instant unregistered SBR. I've seen this one with my own eyes... Many are not aware of the 16 inch minimum barrel length rule.
That being said, you could do it if you did the paperwork, because it is my understanding that you can legally make a pistol into a rifle, but not a rifle into a pistol.