Combine beef, pork, vinegar, 1 teaspoon salt, 1/2 teaspoon pepper, and water in a Dutch oven; cook over low heat about 2 1/2 hours or until meat is tender. Drain, reserving liquid. Shred meat with a fork.
Cover dried corn husks with hot water; let stand 1 to 2 hours or until softened. Drain well, and pat with paper towels to remove excess water. (If husks are too narrow, overlap 2 husks to make a wide one. If husks are too wide, tear off one side.) Use an 8- x 8-inch aluminum foil square for each tamale if dried corn husks are not available.
Sauté garlic and cumin seeds in 3 tablespoons shortening for 5 minutes. Add shredded meat, 1 cup reserved meat broth, 1 tablespoon chili powder, 1 1/2 teaspoons salt, and 1/2 teaspoon pepper. Cook, uncovered, over low heat 30 minutes, stirring occasionally.
Combine corn masa, 1 1/2 teaspoons chili powder, and 3/4 teaspoon salt in a large mixing bowl; stir well. Add 1 1/4 cups reserved meat broth and 1 1/2 tablespoons shortening; mix the dough well.
Place 1 tablespoon of dough in the center of each husk; spread to within 1/2 inch of edge. Place 1 tablespoon meat mixture on dough, spreading evenly. Fold sides of husk to center, enclosing filling completely. Fold pointed end under; tie with string or narrow strips of softened corn husk.
Place a coffee cup in the center of a rack in a large pot. Add just enough water to fill pot below rack level in order to keep tamales above water.
Stand tamales on folded ends around the cup. Bring water to a boil. Cover, and steam 1 1/2 hours or until dough pulls away from husk, adding water as needed.