Salt and pepper the beef shank and beef short rib.
In a large pot, add water and bring to a boil.
Add the beef shank, beef short rib, ancho peppers, guajillo peppers, roasted tomatoes, whole cloves, cumin seeds, black peppercorns, garlic cloves, Mexican oregano, marjoram, sliced onion, Mexican cinnamon, and white vinegar.
Cover and simmer for 3-4 hours or until the meat is tender and easily falls off the bone.
Once the meat is cooked, remove from the pot and shred using two forks.
Strain the remaining liquid and reserve for dipping the tacos.
Heat a skillet over medium heat and warm the corn tortillas on each side until pliable.
To assemble the tacos, place a scoop of the shredded beef onto each tortilla and top with Oaxacan melting cheese.
Fold the tortillas in half and cook in the skillet until the cheese is melted and the tacos are crispy.
Serve the tacos with the reserved dipping liquid on the side.