The lighting on and around the wagon that delivers the gold to the mint changes several times from shot to shot.
According to the reward posters, $150,000 worth of gold was stolen. In 1865 that would equate to 7,500 one ounce $20 gold coins or 469 pounds of gold - far more than could be contained in the two small strongboxes and moved so easily.
There is no attempt to disguise the fact that most of the on screen lamps in this production are electric. No bulbs or cords are visible, but such very steady brightness could not be generated by flames or gas. Incandescent light bulbs had been demonstrated by 1865, but were not in general commercial use until much later in that century. Likewise, the set lighting for both indoor and simulated outdoor shots make no attempt to minimize obvious shadows from electric spotlights.
After Johnny announces he and Sue just got married (without any proposal or ceremony), a frustrated Sue says "General Sherman was right. War IS hell!" This story takes place in 1865. General William Tecumseh Sherman did not say those words until 1879.
When Orbison fires the shooting guitar, his partner says he could play the 1812 Overture on it. Tchaikovsky's 1812 Overture was not composed until 1880.