Trim fat from meat. In a small bowl combine salt, pepper, celery seeds, onion powder, garlic powder, cloves, and cayenne pepper. Sprinkle mixture evenly over all sides of meat; rub in with your fingers.
For a charcoal grill, arrange medium-hot coals around a drip pan. Test for medium heat above pan. Place meat on grill rack over drip pan. Cover and grill about 4 hours or until meat is very tender. (For a gas grill, preheat grill. Reduce heat to medium. Adjust for indirect cooking. Place meat on a rack in a roasting pan, place on grill rack, and grill as above.) Remove meat from grill; cover with foil and let stand for 30 minutes.
Meanwhile, for sauce, in a large saucepan combine tomato sauce, ketchup, onion, sweet pepper, vinegar, brown sugar, Worcestershire sauce, mustard, chili powder, and garlic. Bring to boiling. Reduce heat and simmer, covered, for 15 minutes.
Shred pork with 2 forks. Stir shredded pork into sauce; heat through. Spoon pork onto toasted rolls. Makes 12 to 16 sandwiches.