I'm really into the idea of putting together a retro build and am looking for a bit of advice. My first question was, is there any difference between a Colt 603/M16A1 front sight and the standard A2 sight, either functionally or cosmetically? My second question is if no difference, would I be better off to find a barrel with the A2 front sight already attached? I want to go as close to correct as possible without too much headache. I realize that AR parts are a bit difficult to come by right now but I can't even find a listing for a pencil 20" barrel with the sight attached. Anybody have any tips, thoughts or suggestions?