Get a nodak spud retro upper like this NDS-604. http://www.nodakspud.com/images/NDS-604a.JPG
Now, if you've gotta have the A2 sights and shell deflector, you'll need to hunt down one of these rare, expensive, Colt LMG uppers:
http://img.photobucket.com/albums/v1...n/IMG_0222.jpg

