For ginger scallion sauce, in medium bowl, mix onions, ginger, oil, soy, vinegar and salt. Refrigerate, covered, up to two days. Serve at room temperature and stir before using.
In small bowl, stir together ssamjang, gochujang, vinegar and oil until smooth. Refrigerate, covered, up to two weeks.
For pork, place pork in large bowl.
In medium bowl, mix together granulated sugar and half cup of salt. Rub all over pork. Cover bowl with plastic. Refrigerate six to 24 hours (brush off any extra cure).
Transfer pork, fat side up, to large roasting pan and . Roast in a hot 300 degrees Fahrenheit oven, basting regularly with pan juices, until meat is tender and shreds easily, about six hours. Remove from oven.
In a separate bowl, mix together the remaining salt and brown sugar. Rub the top of the pork. Crank the temperature to 500 degrees Fahrenheit or turn to broil. Return pork to oven. Cook until sugar melts and starts to crust and the fat starts bubbling, five to 10 minutes. Check carefully and mind not to burn the meat or pan. Let it sit 10 minutes before serving.
Serve pork on platter or large plate with forks to shred apart.