I'm currently assembling something along the lines of what you're looking for. My particular effort is being built along the lines of a 604/Air Force model.
Parts I'm using include:
• 20" barrel with triangular handguards and three prong flash hider from
CMMG
• Slick side (no forward assist) A1 upper receiver and A1 hand grip from
Fulton Armory (they also have A1 buttstocks)
• XM16E1 lower receiver from
NoDak Spud
• Anodizing of upper, charging handle, trigger guard, mag release button, sight windage wheel and port door to match the NoDak lower's XM Grey by
US Anodizing
• Flat delta ring, small rectangle port door, round sight post, dimpled selector switch and ramped bolt catch from various purveyors of retro parts on
Arfcom's Equipment Exchange
• A1 buttstock w/o trap door from
Moore Militaria
While I'm not using one, you can also get a slick side chromed bolt carrier from Fulton Armory. There are a few other sources (like
Retro Black Rifle); I've just listed the ones I've used. As mentioned above, Arfcom's retro forum can be a great source of info and suppliers.
Mine awaits the arrival of parts right now:
I'll post a pic in a week or so when it's complete.