I don't know the answer to your question but from what I've read, generally rear discs require 15 inch wheels. I converted an 8.75 to discs using the 94-04 Mustang based setup and assumed I would need 15 in wheels.
Much to my surprise I found 14 in Magnum 500's clear the caliper but 14 in steel wheels - no way. Guessing it's the way it's constructed makes it possible.
