Ultimate plan is to assemble a AR SBR, I have a 10 inch upper and no lower, lower came up that is assembled with stock. Is it still illegal to remove stock and make it a pistol lower? I have a pistol tube ready to go with brace. Wasn't sure if this law changed with lowers no longer having to be marked "pistol only". I have tried finding reference to law unsuccessfully. Can anyone help? Thanks!