I'm running OEM LS1 rotors/calipers with Hawk HPS pads on all 4 corners, LT1 MC and LT1 ABS block currently. The brakes have been bled thoroughly.

After searching I could not find the info I was looking for. I seem to remember someone mentioning that the LS1 brake MC is needed when swapping from LT1 to LS1 rear brakes, but I can't remember why. Possibly something to do with a different piston or valving design.