You're right there, Jamie. I'm not positive, but the Forrest trooper was probably played by Ben Johnson. In "She Wore a Yellow Ribbon" Johnson played a former Confederate Captain named Travis Tyree. Apparently someone liked this name very well, as it was assigned him in two other movies. In Ribbon or Apache there was a roman riding scene, where the rider stands on two horses side by side. I have no idea who stunted for Claude Jarman, who played the Duke's son, but I'd bet Johnson did his own riding. He was an Oklahoma ranch hand and champion rodeo rider before getting into the movie biz. (SEE:http://us.imdb.com/name/nm0424565/bio) A back story in Ribbon was that Maureen Ohara, who played Wayne's wife, was a southern belle whose homw Wayne's troopers had burned in the war. She considered McLaglen an arsonist.
BTW, Slim Pickens was a former rodeo clown, so knew his way around a bull. Stan