ok, and i'm going from memory here, the upper is marked on the side - under the flat-top, with a wierd symbol that looks a cross between an "A" and an "F". also, on the front-face of the reciever, between flat-top and delta ring area should be a small "4".
-about the stock, the package mine came in was marked: Colt buttstock, 4 pos., M4. it has an aluminum buffer tube, M4 buffer marked "H" and a plastic stock piece. BUT i looked at a friend's brand new, Colt 4 position stock (non-M4), and it was identical.
as always, any corrections/amplifications are appreciated!!! hope this helps!