OK, guys can correct me if I'm wrong. I just replaced my parking brakes. The only adjustment I see is a "star" wheel inside the drum parking brake assembly. There is no exterior cable adjustment that I saw on quick look. There is supposed to be an adjustment port or hole in the backing plate but mine is closed off - it looks like the metal knock out plugs on metal electrical boxes. My apporach is to adjust as best I can while assembling the brakes by moving the star adjuster to just barely hear the scraping shoes. There is another hassle you'll have with word rotors on the rear. My advice is to always replace these when doing a rear brake job.
Good luck!
Tom