Although the real Buffalo Bill (Buffalo Bill Cody) and Wild Bill Hickock claimed to have won their spurs as young Pony Express riders, there is no evidence that they ever worked for the company.
Porter Hall, who plays Jim Bridger in this movie about Buffalo Bill Cody (aka "Buffalo Bill") and Wild Bill Hickok, played gunman Jack McCall who murdered Wild Bill Hickok (Gary Cooper) in The Plainsman (1936).