I bought a former police SP1 with a 1968 serial number. Still has the edgewater buffer( yesssss) a newer CS marked A1 length A2 type stock and a replacement M16 bolt carrier marked with an N with an early chrome gas key ( no step), MP marked bolt.
National Aerospace was the manufacturer of the carrier from what I found, but I can't find anything else, like years used etc. Anyone have any info?