Then below that is Jack Ruby. At the time, his neck was pretty "dirty" with scruffy hair growth.
That obviously can't be the same neck either. So, neither the tall nor the short "Ruby" in the garage was really Jack Ruby. Jack Ruby was not there at the time. Jack Ruby was already sequestered on the 5th floor when the garage spectacle took place. Then, they brought him down to mingle him into the scene in the jail office, to make it look like he had just been brought in, but they forgot all about his jacket.