Is it too late to change the thread title to Colt 601 Build...?
Found a correct windage drum (repo) with arrow from AR15SPORT.COM - super pleasant guy to talk with and helped discover what I have is an original Colt 601 upper. I hope to find a method to remove whatever black paint was used to cover the original grey anodizing. After that to do justice by finding the best available option for a lower receiver.
Dick
P.S. excellent link - found good info on the 601 thanks Jim