I've commented on this before, it seems intriguing and a good way to balance several priorities when modeling the 1870s. It seems like the same set of problems originally encountered by British modelers who wanted HO scale equipment and produced British OO as a result.
Another nice thing: Airfix has several "Wild West" themed miniatures sets in OO scale.
My only experience modeling an 1870s scene was a static model, and that was a special circumstance--I didn't have to provide locomotives, as there were some brass V&T locos available to complete the scene.