[quote=it's Bob]The problem with the rear rotors is that the parking brake friction surface is inside the rotor hub. The disc caliper has no function with the P brake as most modern rear disc cars do. You cannot replace the rear rotor with a hat and disc combo and keep the P brake. To do that you would need a new caliper and now you need a new mount and now you have to completely redesign the whole mess. Or call Dr Diff/Cass and use one of his kits.

You could always plumb in a hydraulic brake lock valve.