Okay, for the most part everything here will get the job done. However, I always check headspace, and yes, it can be adjusted on am M16. For the most part it never needs to be. But with the large number of different manufacturers of parts, and the extremes of tolerence, it is not unlikely that sooner or later you will run across a gun that needs to be adjusted.
Bob Dunlap (who used to run the Gunsmithing course at Lassen College) and I had a long talk about this a couple of SHOT Shows back. I use the question of adjusting headspace on the AR type rifle as one of the ways I judge a gunsmith. If they can't answer, they don't get to touch my guns.
It does require special tools though. I have one in storage somewhere based on a design Bob worked out. I've never seen one for sale though.