Non-numbers matching picked up at LGS back in December, 2014.
Receiver, receiver cover: 67476 (No arsenal markings that I can find)
Magazine, trigger group, bolt carrier: 57476
Bolt: 7476
Gas tube: 6333 2446 (might also be 4446 - looks like whoever electro-penciled it in might have tried to fix it)
Gas piston: 4476 6333
Pinned rear sight, sling swivel on left side of stock. Two trap doors in stock (No markings).