The film is explicitly set in the summer of 1863; Custer was not in Kansas at that time, as this film says he was, but more than 1000 miles east of Kansas in Pennsylvania, leading his Union cavalry unit in the Battle of Gettysburg.
The 'backward cant quick draw' holster that the Golden kid wore had not been invented...came about during the 1950s.
Custer, when seen, was wearing 5 stars. 'General of the Army'. The rank wasn't created til WWII, I believe....but was used retroactively, at least for George Washington.
When John Golden throws four bottles in the air for J.R. to shoot, only three shots sound and only three sounds of glass breaking are heard (and only two bottles are shown being shot), but J.R. acts as if he got all the bottles.
Only the syphilitic and those with eyes extremely sensitive to sunlight wore sunglasses before the turn of the 20th century. Custer was neither.