I have fit 323mm (12.71") under OEM TT rears w/ Wilwoods. It clears on jackstands, I'm not sure if it clears after expansion and flexure. It's pretty tight. I drive w/ 17" slicks, so I have plenty of clearance there. I don't think you'll get 13" under there.
Later
When was the last time you *really* did something with your Z to call yourself a Z enthusiast?