Scaly, do you mean when porting adventures written for other systems to Hyperborea? Or more like a FLAILSNAILS game with characters from all sorts of systems? I haven't experienced the latter, but I probably wouldn't address it at all except in that the locals might be all sorts of swordily freaked out to see a dwarf (monster), elf (MONSTER!), or halfling (dinner) ordering a drink at the Pict's Pact.
In the former, I think I've made dwarves into subterranean Kimmerians. Halflings I make either common stock or mules. Elves: Atlanteans or Hyperboreans. For Slumbering Ursine Dunes, I made the cave dwarves into Pygmies.