Oh, well you failed to specify front or rear at the start of your thread, as you nelgected to specify 4 or 5 lug. You simply said your calipers and rotors are getting bad, then said you were thinking of upgrading, so I suppose I assumed that you were talking about front and rear. Are the pads wearing evenly? Do your brakes get so hot your wheel gets hot too? What are the condition and age of your calipers? What exactly are you doing when you "replace your brakes"? Did you machine your rotors? The more info you provide, will result in more accurate diagnosis. I've never heard of anyone just upgrading the rear though if that's what you're doing, but it would be possible. Anyway check this out, should answer your question about the rear z32 brakes, along with the front, & master cyl. on the same page.
http://importnut.net/300zxbrakeswap.htm
My front set up is new 30mm z32 aluminum caliper, ss lines, custom intermediate hardlines, kvr cadmium blk rotors, kvr pads, all new oem hardware.My rear set up is stock s14 caliper, kvr cadmium blk rotors, hawk pads, ss lines.
Based on the current minimal info given, my recommendation is- either disassemble rear calipers to see condition if pistons, and if ok rebuild with new dust boots, and square-cut o-rings. Or simply get new calipers. If you have to get new rotors, then get new pads too. If your having problems, then best to start out fresh.