that's a question that is better left for the law thumping people. There are lots of talk of the "the preban receiver HAS TO BE IN ASSAULT RIFLE FORM before the BAN OMG" talk.
However, fixed stock trunnions (with tangs for wooded butt stocks) readily accept romanian, egyptian, and east german crutch folding stocks. All three of these stocks existed in mass quantity in the world before 1994. They also existed in the United States. So there is no telling whether an enterprising owner bought one and shoved it on the rear of his preban polytech, classic, or norinco and then decided to replace the original wood stock after determining that the cheek weld was absolute shit.
So law thumpers will cry "OMG THERE IS NO PROOF YOU ARE SO ****ED" while I would probably take another stance.
Safe route: preban chicom folder. It was built that way. But get ready to pay $2,000 in MA if you can even find it.