Rally Pack question

I recently purchased a 65 mustang 'C' code fastback. It came with a Rally Pack but I don't know if this is stock or not. The guy who had the car before me tried to turn it into a gt. Is there some code in the vin or some other way I can tell if this was stock or not? I have a book to decipher the vin but I couldn't find anything about the rally pack. Any help would be greatly appreciated. Thank you.