In his autobiography, Gene Wilder says that John Wayne was offered the part that was eventually played by Harrison Ford. Wayne loved the role and was eager to work with Wilder. However, an agent tried to offer Wayne less than his usual fee and the legendary actor turned the film down. This may be true, but it is actually unlikely. By 1979 Wayne was too ill with stomach cancer to consider film work, and in fact he died later that year from the disease.
The horses which Tommy and Avram ride into San Francisco are different from the horses in earlier scenes, which were smaller and used for galloping for long distances. The horses in this later scene are of the breed called American Quarter Horses. You can tell this because their heads and faces are smaller, while their bodies are larger and more muscular, and their rumps (which Avram would call the tuchas) are much rounder than the rumps of long-distance-running horses. The Quarter Horse is very swift for a short distance; the earlier horses, perhaps of a mixed breed, were used for their stamina and placidness.
Some viewers have complained that the name Darryl is anachronistic. One etymology source says that, as a first name, it was not used by English speakers until the late 19th century. However, the name comes from Old French "d'Airelle," meaning someone from the town of Airelle in France; Airelle itself means "open space," from the Latin, so it might be quite old.
The trivia item below may give away important plot points.
At 16:30 having finally found his suitcase after being thrown out of the Wagon, Avram exclaims, "This you couldn't throw out first!?" When in actuallity his suitcase was thrown out first and he was thrown out from the wagon last.