Preheat the oven to 350°F.
Place the guajillo, chiles de arbol and pasilla de negro peppers directly on the oven rack for 5 minutes to toast. Remove from the oven, pull off the stems and pour out the seeds.
In a medium saucepan, place the toasted and de-seeded peppers, garlic, onion, water and salt and bring to a boil. Cook for 20 minutes, until the peppers are soft. Transfer to a blender and purée until smooth. Add the achiote paste, vinegar, cumin, salt and oregano and blend until smooth.
Coat the pork in the spice paste and marinate overnight.
Preheat the oven to 400°F.
Place the onions in a large braising dish. Place the marinated pork on top and roast for 20 minutes, until browned.
Remove the braising dish from the oven and reduce the heat to 300°F.
Add enough chicken stock so that the liquid comes just halfway up the sides of the meat, cover the meat with aluminum foil and the pot lid and cook for 3-4 hours, until the meat is very tender.
Remove the meat from the braising liquid and shred with two forks, adding braising liquid as necessary to moisten. Season to taste.
Heat a grill to high heat. When hot, sear the pineapple rings on both sides for grill marks. Let cool, then dice the grilled pineapple. Toss with the red onion, jalapeño and cilantro in a bowl. Season to taste.
Divide the spicy pulled pork between the tortillas, top with grilled pineapple salsa, cilantro and lime.