WBRM is closer to Conan, Stormbringer, and Lord of the Rings in terms of setting. There are less chieftancies and more kingdoms, most if not all of the factions are iron age in technology, there are traditional mounted knights, roman legionaries, nomadic barbarians, late-stage mongolian barbarians, bandit kingdom, and then your basic fantasy troll kingdom and a touch of the weird like the crimson bat, the dragon newts, stonemen, and shaker cult. What I enjoy the most about it is that it maintains a pretty strong separation of civilization vs weird fantasy; where the civilizations are fairly mundane and historical based, while the fantastic is a constant threat on the borders.
For example, some of the changes I noticed were that Black Horse County has mounts that are alien-looking hellhorses, and are no longer knights. The other is that different books and games are talking about these cultures in disparate parts of history. It's difficult to figure out if the lore is talking about Dragon Pass during the hero wars or during an earlier stage of settlement when perhaps everyone really was from different bronze age tribes and smaller settlements. The use of the word "tribes" and "chieftains" denotes a lower level of civilization, technology, and population. The maps are different for later versions of the area as well, and it is confusing to try and pick and choose what should apply to my campaign.
I've settled on forming a core of the campaign around the lore that is present in the Dragon Pass rulebook (can't get a hold of a WBRM rulebook but I hear there is a mini-comic or something in there which is awesome). I need a little more info to create a list of gods, what they represent, and make a determination of law, neutral, chaos alignment (in Poul Anderson terms); and maybe any additional lore bits if I see anything. I'm perfectly fine for making up my own dungeons and lore for anything not described in detail; in fact I prefer the campaign setting to be a set of guidelines rather than defined to the nth degree. To be clear, I like most of the Nomad Gods content, I just don't like that in Dragon Pass the Praxians ride horses, while in Nomad Gods they ride their clan animals. I could understand each tribe herding a specific type of animal, but riding them seems like a bridge too far.