Just ordered a set of Mustang Rear calipers:
They look a lot like the svt rear calipers but they are a little bit bigger.
They should be able to use the standard ebrake cable setup as well.
I will have to have custom hats and brackets made by wilwood
Benefit being I can now use vented rotors instead of solid which should cool a bit better on the track. I will probably have these done in silver to match the brembo fronts.
I believe this is a similar setup to the htp car that was being built: