Howdy, Marshal! Here's some thoughts on playing Deadlands in the realm of Quelmar. Specifically, we're talking Deadlands: The Weird West, essentially the "third edition" of Deadlands that runs on the broader system Savage Worlds: Adventure Edition. Spoilers exist here, so if you're a player in Brightwater, you should git goin right about now.
Adapting Deadlands
Setting
Pteris is the best fit for tradition Deadlands games. If you go too far west, it might look more like a sandy desert than the American west/southwest, but that geographically hasn't been sharply defined. The monsters out west make it an almost perpetual frontier. The Pacific coast of California can be swapped for the coast of the Kharmaja, the dune sea where sandships sail goods. A sandworm is a nice swap for a maze dragon.
There's two ways to adapt Deadlands in time. You can do it the reasonable way around the 800s PR, with guns and trains existing. DM Kevin actually ran it in the early BR era during the First Infernal Emergence. "Infernal firearms" are the guns of this time, essentially "guns" that ran on devil magic that disappeared at the end of the Infernal Emergence. Trains aren't a thing, but a particularly crafty necromancer might chop up a sandworm corpse, place train cars in between, sew it back together, and reanimate the worm. (This is a surprise for players, James - no snitching.)
The Great Maze could be set on cliffs on the coast of the "Dune Sea." The Great Northwest resembles the Fiddlehead Mountains. The Great Rail Wars could likely be adapted to the Seven Cities and heads north through the deadly lands to Isonhound.
Ghost rock fever can be adapted into gold fever.
Characters
For races, don't feel constrained to humans like the Deadlands book says. Elves, dwarves, and halflings are in the Savage Worlds book to use. I used Saurian stats for Yuan-ti.
For magic, I recommended first to players the Deadlands styles of Arcana (Mad Science, Blessed, Huckster, Chi Masters). However, I let them pick the general SWADE edge Arcane Background (Magic), since wizards and sorcerers populate the realm.
Be careful around depictions of peoples inspired by Indigenous peoples and First Nations. You don't want to fall into stereotypes quickly. DM Kevin just avoided this altogether to not go astray. You could argue that the absence of indigenous people perpetuates the myth that nobody really lived on the land before settlers came, and you might be right. I'd say it's Quelmar, not America, so it's not a great sin. There are postcolonial, indigenous games out there like the Deep Forest you should totally check out.
For chi masters, Rada was a member of a nomadic martial artist tribe. She was stoic and a chi master as a monk in Dungeons and Dragons 5e. DM Kevin didn't include larger Chinese and Chinese American cultures in his BRs setting. I think there are East-Asian inspired cultures around southern Osugbo and north Amusa perhaps, but I think it would be most fun to have them come from across the Dune Sea. Just again, really try not to be racist, please.
For the Christianish Blesseds faith in Deadlands, I think of how the Infernal Emergence would affect worship for the Quelmar pantheon. You worship a rain god in a draught, you worship a war god in a siege, and lots of people worship a light god during an Infernal Emergence. Pelor-worship is common enough that people might refer to him as the "Father" and such.
