The red-haired boy who briefly chats with Bullock's nephew tells William he calls the large trout down the stream "Jumbo." The word jumbo, in reference to something unusually large had it's first usage in American English in 1897, and stems from the famously huge circus elephant, Jumbo, who was brought to the U.S. by P.T. Barnum in 1882. As this season is set in 1876, it's very unlikely that the word would be common - or even uncommon - parlance at that time.
When 'Mr W' and Mayor Farnham are conversing over the contents of Wild Bill's letter, Farnham walks out of shot while talking and we hear his voice alter as he bends to lift up 'Mr W's' luggage. Yet in the next shot we see that he has not yet reached the luggage.