Bill, if he just sends you a butt stock for pad installation you dont need a FFL. If he send you the wood with receiver you would. Hate the way people want to split hairs. In most regards the receiver is the gun not the barrels or butt stock.

I still laugh when I see countless klunker receivers for sale on EBay which goes against FFL. They wont let you sell empty shot gun hulls, except as a decorative item, and yet you can see entire guns being sold in multiple listings.