I realized just how hard I was making this for myself, and that this really is going to be a different game.
In D&D you gain experience through doing stuff (killing monsters, disarming traps, etc.) and someone has painstakingly assigned a number to every monster, trap, etc. that you can do so you know exactly how much XP you get for everything you did.
On the other hand, games like Deadlands, have no such system. Deadlands gives out XP for generic things like finding clues, killing significant baddies, solving mysteries.
And so I realized, you don’t need to know how many glowing orbs of experience each monster drops. Because that encourages players to open the door, kill what’s inside. (Not that that’s necessarily bad.) If you instead reward the story, which might be, “open the door and kill everything inside”, you can (theoretically) have the best of both worlds.