the only restrictions that i know of are no pistol grip and no buttstock... sorry though i dont have a link for y ou.
The vertical foregrip makes it an AOW, does it not?
I'm looking for an upper receiver in 7.5" to mate with my RRA pistol lower.
maybe that should go in the Want To Buy thread.... the OP was asking questions about legalities, not asking what other people on the board were trying to build.
It's legal. use a buffer tube ONLY and try to get a pistol buffer tube. They are not made for stocks.
DO NOT put a vertical grip on the front. This makes it an AOW.