I've seen people who were interested in putting Cobalt SS Brembo brakes onto Kappas, but seemed that it would not bolt on, at least on the rears, and they may not fit with the stock sized wheels without spacers. But now I just saw this in the SCCA rulebook:
Brake calipers and rotors from Chevrolet Cobalt SS (08-09) permitted - part numbers 25900763 - left front caliper, 25900764 - right front caliper, 25902073 - left rear caliper, 25902074 - right rear caliper, 25869424 - rear caliper bracket, 25994100 - front rotors, 15921402 - rear rotors.
Maybe the rear caliper bracket part 25869424 is what is needed to make the rears bolt on?
For anyone who wants a fancy Brembo sticker on their brakes, this might be the easiest way.
I'm not spending anymore time on this though, because I'm not going to upgrade my brakes. So if someone wants to roll with it and research it, go for it!