It is the wrong forging for an M16. It is an A2 forging. That would be M16-A1 or M16-A2. The Colt pony should be a "floating pony" for an M16. IMHO it is a fake.
Your pic is of an aftermarket aluminum stock.Also, what type of stock? Is it like this?:
http://i1113.photobucket.com/albums/k517/s0b3/20130308_165109.jpg