^^^^ see above post!
the only thing with a serial number that matters, is the lower receiver. with or without an lpk makes NO difference. with or without an upper receiver makes NO difference.
the lower receiver IS THE ONLY part of your AR- that the BATFE considers "a firearm."
in fact, you could order a "fully-loaded AR-15" WITHOUT the lower receiver (meaning you WOULD HAVE EVERYTHING TO MAKE A FULLY ASSEMBLED AR-15, EXCEPT THE LOWER RECEIVER), and would NOT have to go to an FFL holder and fill out a form 4473 to do a NICS check.
"they may get me in a rush, but not before i turn your head into a canoe....." -Kurt Russell (Wyatt Earp) in Tombstone
"if it was up to me, i'd like to see, this country run,
the way it used to be, the way it oughta be, just like it's done, OUT HERE.........WAY OUT HERE." -Josh Thompson, country music singer http://www.youtube.com/watch?v=D0sYnro_3Rc
PEOPLE TEND TO ACT LIKE SHEEP, BOY I LOVE MUTTON! -Me