anti-sway bar question?

I have seen pictures of 66 gto's with and without a REAR anti- sway bar. Does anyone know why?

GTO's did not come with rear sway bars until 1970. If you seen a pre 70 Goat with a sway bar it was not original.

Thanks timmy. Even though the codes on the fire wall and door jamb are accurate for my 66 gto, I thought it might be a really good clone because it was missing the sway bar. You gotta check everything these days when layng out so much cash.