When Harry is in the cabin with the painter, he's asked what year it is. Harry answers 1900. Shortly thereafter Harry says that Black Jack Ketchum was decapitated when hanged. Ketchum was hanged over a year after the time frame of this conversation, on April 26, 1901.
At 1:02 Harry Tracy is pasting US paper money on a wall, but the federal reserve notes are from 1913 at the earliest. A $1 note from 1923 is also visible. Harry Tracy died in 1902.
The "trolley" Harry chases has neither a trolley pole nor overhead electrical wire.
The headline on the newspaper that Harry reads announcing Merrill's betrayal misspells the words "Pursue" and "Trail." It reads "150 Men Persue Bloody Tracy Trial."