There main differences are color, blue / grey or NATO black.
Inside it's either buffered or not. If you have a buffered carrier, then you'd need a non buffered stock,
or remove the buffer from the carrier if you end up with a buffered stock.
Some say don't run two buffers, some say its ok......
Externally, the shape of the buttpad is a difference, the old style looks cooler imho, though the later
style is more comfy ~ either way, have fun finding one, it's a neat accessory, though not the most comfortable
to shoot with. The standard metal ended A2 is the best for it. If you are not a purist, don't forget the Choate
folder, I think they look great on the rifles, and the non adjustable one is spot on for a 80's look.