[Captainfab]

You should be running smaller diameter piston calipers on the rear than are on the front. The 2" bore calipers on the front, and the 1-1/4" bore on the rear

suttoncurt, you were correct, you will need 120-10938 on the rear. The 120-10939 that CPP sent you are for 1" thick rotors. The Astro rotors are 1-1/4" thick rotors. The 120-10936 are 2" bore calipers for 1-1/4" thick rotors on the front.