I'm not sure I quite understand the "change parts but leave it all colt" mindset. I would personally take all the original Colt stuff, pack it up nicely and put modern good parts in it if he wants to shoot. (SSF trigger, etc) If he wants to sell, swap it back over. If he's already swapping a burst gun to an auto, then why not go all the way? I absolutely understand the all original idea if it's a gun for a collection. If he's going to shoot it, have fun and then swap back to the "classic" config. Put some wear on modern parts, preserve the originals. This is one of the fantastic things about a registered receiver--- you can bring it into the modern era with no permanent changes to the gun.