As far as XM16E1's here is my experience. I was with the 82d and we were issued the XM16E1 circa Feb/Mar of 65. (We deployed to Domincan Republic circa April 29) I heard that the 101st and the 1st Cav (late name) were also being issued. The bolts and carriers and all related parts were chromed. The 173d also had these early rifles which the unit brought to Vietnam in May of 65.
We were also issued cleaning rods with 1964 contract dates circa Oct, Nov. The bipods were double lock pin types, not peened. I always thought the production period of the rifles was from late 1964, due to the serial numbers. We had heard about getting these rifles several months before they arrived and from what I was told, all units got them at the same time.
We were warned about the Waffle Magazines and ordered to turn in any that were issued. I saw none at all while in the service. I have seen and owned several from gun shows over the years. I have two different versions.