As far as I know, the rearend in the 93R is a "pull ahead" part, as were the 94GT wheels. Both being pulled ahead of time from the 1994 Mustang production for use on the 1993 Cobra R. Others on here will have to provide more detail about the rear brakes.
The wheel on a 93R hangs out just the same as a fox that has had a 94-98 rearend installed. Ford had the rear fender lips cut for more tire clearence but they still rub the outside of the tire.
I have heard in the past that some people think they are the same as an SVO/Mark7 rearend. I believe they (SVO/M7) are the same as a 94-98 in width though... if not its only like 1/32 difference. If I can find my interchange book it gives the axle lengths of all of them.