A co worker of mine has a 98 3/4ton GMC 4x4. He went to get brakes for his truck at the auto parts store and they needed to know if he had 11in or 9in rear brakes. He didn't have an idea or the time to take them apart. The truck has a 454/4L80E and 3.73's in the rear. I am assuming it will have the larger brakes but am not sure. Any help?

William