You can put SC rotors on the rear if you get longer studs and make a spacer to go between flange and disc. Deep 6's (5 1/2's or 7's if you re-work the body to accept them) are needed when you use the SC disc. The outside diameter of the disc may also need to be reduced by a small amount to accept SWB 911S calipers. SWB 911S calipers are fine when used with SWB 911S calipers in front but if you use larger calipers (aluminum 911S, 911SC or others) in the front then your brake balance will be upset (too much front brake) and you will then want a brake pedal assembly with balance bar, possibly with two different diameter master cylinders.
I know this from personal experience.
