I think you spindles may not be designed to work with the standard D52 calipers you have listed. If you check the Willwood site and put in the info for a C10 with CPP spindles the only options listed are the 6 piston calipers designed for 13-14" rotors. You should probably call CPP for more info. What is the part number of your drop spindles?
https://www.wilwood.com/BrakeKits/Br...2+Drop+Spindle