Might be a case for contacting ATF-I would think it's only "manufacturing a post '86" if you modify the RDIAS as it's the part considered a machine gun,and can be moved from "host rifle to host rifle" , but don't take that as advice, people have been arrested for much simpler things firearm related. One thing to keep in mind before modifying your rifle to make it fit, though, is whether FA carriers are available for the AR10. If M16 carriers will fit it's not an issue, but if they won't I have never seen a FA carrier to fit the AR10.