Place the pork in a large,shallow bowl. Mix together the sugar and 1/2 cups of the salt in another bowl, then rub the sugar-and-salt mixture all over the meat. Cover the pork with plastic wrap and place the refrigerator for at least 6 hours or overnight.
When you're ready to cook, preheat the oven to 300 degrees. Remove the pork from the refrigerator and brush off the sugar-and-salt mixture. Score the fat cap of the pork butt in a crosshatch pattern, place the pork in a roasting pan, fat side up, and roast for approximately 7-8 hours.
After the first hour, baste hourly with the pan juices (I have not done this). After an additional 5 hours, remove the meat from the oven. Stir together the chili powder, cumin, garlic powder, red pepper flakes, oregano, paprika, the remaining 1 teaspoon of salt, and the black pepper and sprinkle the spice mix over the top of the roast. Place the pork back in the oven and let it cook for another hour or so. If the spices start to burn, tent the pork with aluminum foil. The meat is done when it's super easy to tear apart with a fork. It should basically collapse when you try to pull it apart
This part is optional I have skipped it and still turns out great -To create a crust, turn up the oven to 500 and juice then juice the limes and oranges over the pork. Roast the pork butt for another 10 -15 minutes, until a caramel crust develops on the meat.
Serve hot, with accoutrements. Invite diners to create lettuce wraps with pieces of the pork and whatever toppings they desire.