A while back ATF came out and declared that thumbhole stocks like those on the Romanian and Bulgarian post ban imported AK's now constituted a pistol grip......which is why the thumbhole stocked post ban imports with standard magazine wells were stopped from importation.
There's something going on....the FS-2000 uses M16 magazines and if you use USGI mags, that's three US parts right there, so they probably only need a US op rod, piston, trigger pack, etc. to be legal.