Nice. Retro builds are fun and these days, expensive. Apex Gun Parts tends to have some of the correct lower parts. I know they have A1 grips that are in good shape. Pretty sure they have m16 selectors too. A1 sight assemblies for your stripped uppers can be found on gunbroker. Good luck with the a1 port doors. Pricey when found. Check out US Collectors Ordnance for buttstocks and proper slings. Real retro colt bolt groups are expensive. Apex has them if you are willing to pay. For the price I'd just put in a quality modern BCG.