Place the potatoes in a large pot of cold water. Add the salt, bring to a boil and cook until tender, 20 minutes. Drain the potatoes and set aside.
Place the pork in a large pot of cold water. Add the onion half, the garlic, and the bay leaves. Bring to a boil then reduce the heat to low. Simmer gently until the pork is cooked through and is no longer pink in the center, about 45 minutes. Remove the pork from the water and set it aside until it is cool enough to handle (discard the cooking liquid). Using your fingers or 2 forks, shred the meat into small pieces and set aside.
In a large skillet over medium-high heat, saute crumbled chorizo until completely cooked through, 8 to 10 minutes, stirring often. Using a slotted spoon, transfer the chorizo to a paper towel lined plate. Add the chopped onions to the chorizo skillet and cook until soft, about 3 to 5 minutes, stirring occasionally. Add the shredded pork, the tomatoes, and the chipotle chiles. Cook until the tomatoes break down and release their juices, about 5 minutes. Return the potatoes and cooked chorizo to the pan. Stir in the vinegar, thyme, marjoram and salt, to taste. Continue to cook over medium heat until some of the liquid has evaporated, about 5 minutes.
While the pork cooks, heat a medium skillet over medium-high heat. Add a tortilla and warm for 10 to 15 seconds. Flip the tortilla over and continue to warm until the tortilla is pliable and heated through, another 10 to 20 seconds. Place warm tortillas in a tortilla warmer or on a plate, cover with a kitchen towel, and set aside; repeat with the remaining tortillas (or warm the tortillas in the microwave: stack them on a plate and cover with a damp cloth; microwave for 30 seconds and keep them covered until you're ready to serve).
Place the pulled pork in a serving bowl or bring to the table in the cooking pot. Arrange the limes, avocado, and cilantro on a platter. Pass warm tortillas so each diner can fill a tortilla with some of the meat and accompaniments. Squeeze lime juice over each serving.
Recipe courtesy of Ingrid Hoffmann, 2008