Cook the pork. Cover meats with water about 8 quarts. Add 1/4 cup salt and one large head of garlic cut through the equator, no need to peel. Bring to a boil, reduce to simmer. Skim off foam and simmer, covered for about 3 hours, until tender. Check from time to time, you may need more water. Cool slightly, then remove the meat. When ready to handle pull meat off bones, discard all bones, fat and skin. You can scoop out the onions and add to the pulled meat along with the garlic head. Squeeze out the pulp from the head of garlic and smash it with a fork, add it to the meat along with the onions, discard the paper skin from the garlic.
Refrigerate the broth. At serving time scoop off the fat from the broth (it will be very gelatinous ) add 1/4 cup ground chili d arbor to broth along with the corn. Bring to a boil then simmer. Taste for salt.
Reheat the meat, covered with foil in the oven 300 degrees. You're just warming it. You may want to ladle some broth over the meat just to moisten it before you put it in the oven.
At serving time set out the pot of very hot broth, the warmed pork, and classical garnishes listed below. Your guests help themselves to the meat, putting it in a bowl, pour over the broth with the corn and garnish as they like. All you need now is some cold cerveza or sangria. enjoy.
Garnishes are typically, tostadas or corn chips, chopped rinsed white onion, radish slices, chopped fresh cilantro, lime wedges, fresh chopped chills (serrano or jalepeno) avacado slices, dried ground chile d arbor and dries mexican oregano.