Ben Johnson worked on Oklahoma as a stunt man, wrangler and extra. It was the only work he was able to get after being away from Hollywood for more than a year pursuing and winning that world roping championship. At the end of the year, he was flat broke, despite his winnings, because he had paid the entry fees and expenses for his team roping partners and anyone else who assisted him.
On Oklahoma, he taught Gordon MacRae how to ride well enough to look OK on camera. He doubled for Rod Steiger in the runaway wagon scene. I suspect that's him jumping from the train to the horse far off in the distance at the end of the "Kansas City" number but it's impossible to tell.
As an extra, he is very clearly seen in the "Kansas City" number. In long shot, at the right hand side of the frame, he gallops up to the station with an extra horse he's bringing for the returning Will Parker, and then you can see him on the left hand side as one of the cowboys listening to Will sing about Kansas City, finally exiting to the right as the dance portion of the number begins. Ben also is one of the people who rushes up to Jud's shack after he and Curley shoot off their guns.
He also rented cattle to the production.
Two publicity stills from the "Kansas City" number.
A screencap from the shooting scene at Jud's shack. Ben's on the left again.
