Thordsen customs has come out with a GEN III FRS-15 featureless stock for New York compliance that New Yorkers might like.
This new design builds on what they learned from previous versions and through customer feedback. It offers a better look. You can order it with the buffer tube cover, or keep the buffer tube cover from your old Thordsen stock and just order the stock portion. At first it may look like a thumbhole stock but the stock and buffer tube are not connected. You can see more here:
https://www.youtube.com/watch?v=S_88lumNmIo&t=0s http://www.thordsencustoms.com/frs-15-gen-iii-rifle-stock/