At least 6 hours before cooking, make the marinade: Heat a heavy griddle or frying pan over medium heat and gently toast the chiles, pressing them down quickly with a spatula. Turn and repeat on the other side. Be very careful not to scorch the chiles or they will have an off taste. Cool and then remove the stems, seeds, and stringy ribs.
Tear the chiles into small pieces and pulse in a spice grinder until they are as finely ground as possible.
In a blender, combine the garlic, vinegar, achiote, salt, cumin, and cloves. Puree until well combined. Add the ground chiles and blend for several minutes, or until the sauce is very smooth; if necessary, add a tablespoon or so of vinegar to make a thick paste.
Heat the oil over medium heat in a frying pan. Add the onion and cook, stirring, for 1 minute. Add the chile paste; use the water to swish out the blender and add to the pan. Cook, stirring, for 3 minutes, or until thickened. Scrape onto a plate and cool completely.
Cut the pork into lengthwise slices about 3/4 inch thick and smear a layer of the chile paste on each side (thick enough to draw a line in). Stack the slices in a shallow container, cover, and refrigerate for 6 to 12 hours.
Cut the crown off the pineapple and cut a slice off the bottom. Carve off the prickly skin, slicing from top to bottom, then cut the flesh into slices 1/2 inch thick; set aside.
Grill Method: Half an hour before cooking, clean the grill thoroughly with a brush and wipe it down with an oil-dampened rag. Preheat the grill on high. Remove any thick blobs of chile paste from the meat, as these will burn. Grill the meat and pineapple for 7 minutes on each side, directly over the flame (if your grill is hot as heck -- medium is ok). Watch carefully to make sure the chile paste is not burning; if needed, turn down the heat or move the meat to a cooler part of the grill. The pineapple should be given a half-turn partway through cooking to make nice crosshatch marks. When the meat is cooked to an internal temperature of 145 degrees (don't overcook) remove to a warm plate.
Oven method: Preheat the oven to 375°F Spread the meat out in one layer in a shallow, lightly oiled baking dish or a rimmed cookie sheet. There should be some open space between the pieces; it's better to use several baking dishes than crowd the meat. Cut half of the pineapple slices into quarters and scatter over the top. Reserve the rest for another use. Roast the meat and pineapple for 30 to 40 minutes, or until well browned and crisp; there should be some caramelized juices in the bottom of the dish. Remove from the oven, cover the cooked meat and pineapple loosely with foil, and let stand 5 minutes while you heat the tortillas.
To Serve: Heat the tortillas' keep them warm in a cloth napkin or a tortilla warmer. Dice the meat into small bits, mix with the juices on the plate or in the baking dish, and fill the tortillas. The pineapple can be chopped up or cut into quarters. Serve with the onion, radishes, cilantro, and your choice of salsa or hot sauce.