Lots of great info at the below link in general about making an NFA weapon.
http://www.guntrustlawyer.com/shortb...shotguns-sbss/
Note there is a size and type of font requirement that has to be used for your engraved info. (Sans Serif style font, 1/16" tall, and .003" deep IIRC - but verify this)
Regards,
Rob