ok, this is my first try at pics, so bear with me......now, financial reasons preclude real colt parts for this one, [hopefully later I can try and piece together some real parts for another build]

ordered a Fulton Armory A2 upper and then the parts to complete it, when I got it it was rough looking but I wiped it down with clp and it looked a lot better, last pic is after assembling the sight / forward assist / ejection port door / and charge handle
I have a "no rollmark" Range Tool lower / DPMS A2 buttstock for this build, not put it together yet and plan on using a Windham
Weaponry 20/; govt profile barrel kit as recommended by several members here and parkerized bcg

You have a good start. You have also made a wise decision to get the Windham Weaponry 20" Gov't profile barrel. I one on my A2 and A4 clones. Very accurate. If you are in need of the A2 stock, check with White Oak Armament/White Oak Armory. I bought mine through them. Very nice stock. Also, if you get the Windham Weaponry barrel kit, it comes with everything you need (barrel assembly, Delta ring assembly, handguards, FH, and gas tube and roll pin).

http://www.whiteoakarmament.com/xcart/product.php?productid=17592&cat=282&page=1

http://www.windhamweaponry.com/shopexd.asp?id=318#axzz3loGYSOfD

Check the EE for some A2 furniture. You might be able to save some $$$.

delete

that's where I got my rear sight assembly , I will have to keep looking