1. Combine whisky and salmon in a large zip-top plastic bag. Refrigerate 1 hour, turning occasionally. Drain; pat salmon dry.
2. Combine brown sugar, pepper, salt, and rind in a large bowl. Place one-third of sugar mixture in bottom of an 11 x 7inch baking dish. Add fish; top evenly with remaining sugar mixture. Cover with plastic wrap; refrigerate 4 hours. Rinse fish well; pat dry.
3. Soak grilling plank in water 1 hour; drain. Soak wood chips in water 30 minutes; drain.
4. Remove grill rack; set aside. Prepare grill for indirect grilling, heating both sides to medium and leaving center with no heat. Maintain temperature at medium (325°). Toss wood chips on coals. Place grill rack on grill. Place salmon, skinned-side down, on plank in center of hot rack, away from the heat. Cover; cook 30 minutes or until desired degree of doneness. Serve with cracked peppercorns and lemon slices, if desired.