I always add the Full auto option on receivers I make even if it's for civilian use. It adds value to the lower. I also give my customers an option of a custom serial number, logo on the magwell, or any engravings they wish. Most of them always ask for "For Military or Law Enforcement Use Only"
In other words, it's 100% legal
Delta Firearms Mfg Co. 07/08 FFL SOT 2, Hobby Shop Owner