If you want cowboys instead of mercenaries when investigating the paranormal, ACES is a great place to look. It adds in a good amount of thematic traits for the setting and adds some crunch to ranged combat with reloading mechanics. Perfect for gamers who want a bit of mid combat drama.
The included adventure shows some creative ways to combine the western genre with the more nebulous "paranormal."
If you want to explore different genre combinations with FIST, you should see what ACES can do for your table.