The man directly behind him in the black cap is Kenji Sato. He was K's best running buddy for ages. Ran the Sports Car Club of Japan IIRC. Visiting Kenji's home was a regular stop on the Western Gangster tours to Japan until he passed in 2003.
The guy in the green T shirt is Chris C. He's Dallas local and is one of the Original Western Gangsters (OWG) in 1996 I believe. The guy in the checked shirt is Russell(Dallas) he's also OWG.
Later
When was the last time you *really* did something with your Z to call yourself a Z enthusiast?