I didn't set my sights as high as you for detail, but I am very happy with my purchase. You seem intent on building one, and that's definitely cool, but I already have a 1911 project languishing, and figured I might be just as well off to buy a rifle outright so that its accuracy and function was guaranteed outright, you know? Figure maybe my easy "retro" gun might help somebody else that for whatever reason doesn't want to totally build one.
Anyways, I had found the Vietnam handguard and pistol grip a few years ago here in town at a hole in the wall shop in case I ever got the AR bug. Collection pretty much got "finished," and since I had a near complete Vietnam uniform without a rifle, I figured I knew what to do next. I bought a DPMS Lite 20, and it is pretty close... has the simple left/right rear knob only, like i have seen in pictures, bolt assist, 20" barrel that I assume is a thinner contoured barrel (hence the "Lite" designation?), bayonet lug, etc. All I have to do is score a 3 prong flash suppressor and she's good enough for me at only about $713 for the rifle including tax, and about $10 for the handguard and grip. Only "problem" I see is that it has a black bolt. I am not entirely an early M16 expert, so I don't know which era that would work with, but it isn't significant enough for me to be turned off. Neither is the finish of the gun, which I think is too black for parkerizing, or the rear stock, which is a grayish color, but looks black enough for this guy. I also don't think the barrel is chromed, however. I don't let my guns go more than few days without cleaning (habit that the Mosin, Mauser, and Enfield taught me. Ain't corrosive ammo grand??).
Long story short, mine is "Nam enough for me to call my Vietnam uniform done, touched bullets with ease when setting the 25 meter battle sight, and should be a helluva groundhog/coyote gun to boot.
I did have to fit the 'Nam handguard at the muzzle end, but that upper and mine look VERY close. It just seems like the bulge in the barrel behind the gas block is marginally bigger.