Do a little more research. I believe by law none of the Norinco/Polytech M-14 clones can lawfully have a GI type flashhider. This was due to an import restrictions targeted specifically against China by the Bush Administration in the late 80's, it's got nothing to do with Clinton's 1994 "Assault Weapon" ban. That said, you can still put a Smith muzzle brake on it's perfectly legal.
All the Norincos I've seen simply had the flash hider cut off and the retaining nut tack-welded in place. Use a Dremel to cut the tack-welds, unscrew the nut, and the spines should still be in the barrel underneath. The Smith brake should slip right on, though you may need to buy a new retaining nut. -- Kernel