Appropriate Wheel Offset for 18" Wheels?

Dr. Diff 13 inch cobra front, 8-3/4 big brake kit rear. Stock width A body 8-3/4 currently or B body 70-74 if I can get one in Alaska. Spring relocation in the rear, and will mod the outer wheel well a bit for some clearance if needed.
Tubular uppers, USCT full stiffening kit.