I am Byron Tomingas, and I live and have worked in Jackson Wyoming for many years. I was in several of the Jackson Hole, WY episodes of TCB in 1969. I knew the stunt riders well as I had an early Sportster.
I attached a couple of shots of me with that Sportster (the early flat head version called a K-Model) at the time they were filming Then Came Bronson in and around Jackson. I once saw Keenan Wynn blasting out through the Elk Refuge (dirt road) on his bike.

I also knew the producer Bob Justman and Robert Saboroff quite well, I was a river guide and took them on a float trip. Mr. Saboroff played Flamenco Guitar (I am a classical guitarist with a degree from Cal Arts: www.Tomingas.com So we stayed in touch for many years. Mr. Justman had also produced some of the Star Trek TV episodes.
As you can see, in one of the pictures, I'm still riding a Sportster but this ones a 1200cc, and yes, I still have that old Flathead Sportster. You might see an odd carburetor, it is a big Mikuni pumper off a racing snow machine. The two small gas tanks were brass fire extinguishers that I converted.
The movie production crew usually called VERY early in the morning if they needed some extras, my girlfriend and I had been doing a lot of extra work on the show. I was at her place when they called and she talked to them, I kept saying "Ask if they need me today", several times, she did not. When she got off the phone I asked her if they needed me, she said they did not. That was the morning they were calling everywhere trying to find. I was supposed to ride the bike as it passes the school bus, all the stunt guys were busy on a different scene. Yes, I am still mad at her today, no I did not marry her. In fact, I am REALLY mad at her. 8^)