The Illinois Central Railroad boxcar after the last big fight is painted/blacked-out but its logo can still be clearly identified as the 1967-1972 vintage rather than the depression-era of the movie setting.
Cheney rides into town at the beginning of the film on a train pulled by a diesel electric locomotive that did no exist at the time the film is set. Later Speed and Cheney ride back to New Orleans on a steam train that would be correct for the time.
When the Cajun band is playing on the platform by the river, a paddle-wheel steamboat travels by. Though the boat is clearly moving faster than the current and driven by an external power source, its paddle-wheel is not turning.
While Speed is waiting for Chaney on his balcony, reading the track listings, he is wearing his shirt. The next scene is when he hears the door bell, but he's not wearing his shirt; that is draped over the chair.
When James Coburn is introducing Strother Martin to Charles Bronson, Coburn's arms are hanging loosely by his sides, then the angle changes to face Coburn & his hands are in his pockets. Later in the scene his arms are folded but we never see him fold them.
We see Chaney jump off the train at the beginning, with the next scene showing him walking by tanker cars. In the background you can see the same train that he just jumped from backing up. Most railroaders would know it was a through freight, and not just switching cars.