Per the vehicle kit on GM Heritage Center:
Regular Front: 6.00-20-6, 5" rim, 4-1/8" offset
Regular Rear Single: 32x6 - 8ply, 5" rim, 4-1/8" offset
Regular Rear Dual: 6.00-20-6 ply, 5" rim, 4-1/8" offset
Details about what sizes went with what options are on page 54 of this document:
Vehicle Information Kit
