I'd buy an SBA4 arm brace and forget the registration. As a pistol your AR needs no stamp, can be transported across state lines without letter to the ATF explaining why. It can also be loaded in your vehicle and concealed. In Kansas we don't require conceal carry permits to carry.
https://www.brownells.com/handgun-parts/...prod124972.aspx
They get as low as $100 pretty often.
