No. Once a lower receiver has a stock installed and mated to a rifle upper, it is considered a rifle and cannot be converted to a pistol. It can, however, be converted to an SBR with the proper NFA stamp.
Screwy laws .....This receiver has never been transferred as a long gun.....and its stamped multi cal.....but I guess if someone REALLY wanted to cause you trouble...they MIGHT be able to....but I doubt it.