Steele, Allen. "Riders in the Sky"
Divergence: 1860 CE
What if: The dirigible was invented in 1860.
Summary: Jesse and Frank James become infamous airship robbers, but Northfield, Minnesota, and Bob Ford still lie in their future.
Published: In Alternate Outlaws (ed. Mike Resnick), q.v.; and All-American Alien Boy: The United States as Science Fiction, Science Fiction as a Journey; A Collection, Old Earth 1996 (1882968050, 1882968069), Ace 1997 (0441004601BUY).