I am looking to transfer a complete AR15 carbine to my daughter in Arkansas from here in Oregon. The build is based on a Polymer80 lower that I have milled out. Does anyone know what the requirements are for producing a serial number on it whereby it will all be legal and she can register it thru her FFL? Do I make up a number an etch it into the lower? Or does the receiving FFL do that? Anything else I might need to know? Thanx in advance!