Disc Brake Upgrade

[99silverdenali]

I have a 99 Yukon Denali with the typical weak brake syndrome. Using the wisdom of Forum members, I have decided to upgrade to Powerslot rotors and Hawk pads. When I search for these items, the rotors are dependent on whether you have 10 inch or 11 inch rear end. How do I make sure of which one I have before I order the replacement parts? Any help would be appreciated

 

[SunlitComet]

in these vehicle years 2 doors are 10" drums in rear and 4 door models use 11" in the rear.