NO.  Under 922(r), which the regulations of the '89 ban affected, you cannot add features to an imported rifle that would have prevented the rifle from being imported.  Either a pistol grip or a folding stock would have prevented the importation of the SKS.

Of course, if you replace enough imported parts with domestically-produced parts, the gun will no longer be an "import" under the law, but "domestic."  As long as you kept the fixed 10-round mag, you could add lots of evil features.  If you go that way, make sure you keep every receipt for those parts, so you can prove you replaced them if you ever get hassled.

-Troy

The standard SKS isn't covered by the 1994 Crime Bill because it's not a semiautomatic assault weapon.  That requires a detachable magazine and the SKS magazine is fixed.

-- Chuck