1860s to 1900 is a good date range with the exception of B-Western in which your basing your costuming on Hollywood interpretations from the B-Western era (mid 1930s to 1950 and the RULE BOOK).
I would suggest trying to settle on a persona that you would like to portray (rail engineer, frontiersman, working cowboy, visitor from foreign land, banker, traveling salesman, ect) and then do your research on clothing accoutrements.
Folks in the West were pretty open to wearing whatever was available and functional.
Thinkin' it might be easier that way.
YMMV