1. TO BRINE THE PORK: With sharp paring knife, cut 1-inch-deep slits (about 1 inch long) all over roast, spaced about 2 inches apart. Dissolve sugar and salt in 6 quarts cold water in stockpot or large bucket. Stir in garlic and orange juice. Submerge pork in brine and refrigerate 18 to 24 hours. 2. TO APPLY THE GARLIC-CITRUS PASTE: Process garlic, cumin, oregano, salt, and pepper in food processor until they reach consistency of coarse paste, about ten 1-second pulses. With machine running, add orange juice, vinegar, and oil through feed tube and process until mixture forms smooth, wet paste, about 20 seconds. Remove pork from brine and rinse under cool running water; pat dry with paper towels. Rub paste all over pork and into slits. Refrigerate pork until ready to grill. 3. TO GRILL-ROAST THE PORK: Turn all grill burners to high, close lid, and heat until hot, about 15 minutes. Scrape grate clean with grill brush. Turn off all except primary burner (burner that will remain on during cooking). Place roast with skin side up on cool side of grill, shielded with foil (see photos, below). Close cover and lower primary burner to medium or medium-high (grill temperature should be about 325 degrees). Cook until skin is browned and crisp and instant-read thermometer inserted into thickest part of meat registers 190 degrees, about 6 hours, rotating meat 180 degrees and removing foil shield halfway through cooking time. 4. Transfer roast to cutting board and let rest 1 hour. To carve, first remove skin in one large piece. Scrape off and discard top layer of fat, then cut pork away from bone in 3 or 4 large pieces. Slice each piece against grain into 1/4-inch slices. To serve skin, scrape excess fat from underside and cut into strips. Drizzle Mojo Sauce (see related recipe) over pork just before serving.