So, I got this pre-ban Colt and now I want to make an M4 out of it.

I have seen at a gun show a guy selling a complete Colt m4 upper. It has the barrel cuts, m4 handguard, flatop w/removable handle. Even came with complete bolt and charging handle. $700. I know thats about the going rate for the M4 Colt upper. But how can I authenticate it? Are there any markings that should be on an M4 upper like on the receiver or anywhere else. If so what are they?

Also, I will need a M4 stock. Can I just get the Colt 4 position with the m4 buffer or is there a different one that is specific to the M4?

Can't speak for any specific markings on the upper but I do know the Colt M4 barrels are just stamped

C MP 556 Nato 1/9

Actually $700.00 is a REAL good price if it's all Colt and includes the bolt and carrier...

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!

OK  thats what I was looking for.  Heard they were marked with a 4 or M4 but did not know where exactly.  The AF is not unigue to the M4, the one I saw definetley had that, but so does my post ban gun.  It denotes where it was forged.  AF = Alcoa Forged