Actually, there were so many folks in the "old" USA West from diverse countries in Europe, Scandinavia, Brittania, slavic countries, China, etc. that just about any sort of "old fashined" dress can be documented. From my perspective, Hollywood is a poor example of anything relevant, especially if any sort of "western".
I am begining to think that any item-specific "costume" criteria that NCOWS might have might best be tossed in favor of having the individual explain the relevance of each item in his/her impression. I, for one, was wearing three items of clothing that are very specific to my persona as an immigrant assayer ("fiddlers" cap, bussarong shirt, rough-out gloves), but, not something that many (any?) NCOWS members would have been aware of. There are many more such items that I may add and many, many more personas that can be developed. Try impersonating a Morman cart pusher from Norway on his/her way to Utah, for example. In addition, us immigrants mixed items of our native dress with items available in the 1800s USA.
Lars