Tony,
I believe that the Mark VIIs came with 11" front rotors. Pre-'87 GTs came with 10" brakes, the same brakes as the four cylinder LXs. Ford changed to bigger brakes for a reason. When I did my first brake upgrade, I switched from 10" to 11" rotors. It was incredible the difference in braking performance. If you buy the rotors and find you need the spindles, I still have them, along with some 73mm caliper cores. I never upgraded to the 73mm calipers, but received some with the Mark VII system I bought.
I see a 5-lug conversion for 79-86 mustangs for $119.95 in the back of this months MM&FF, p.291, in an ad for Complete Brake Service Inc. (1-800-581-2339) it's a long running ad. I cannot remember ever not seeing it in there.
Chatcher,
Are the calipers and brackets lighter on the SN95 rears than the Mark VIIs? I have the PBR front calipers and they are super light compared to the 1985 and 73mm calipers. I plan on getting some front Cobra brakes this summer and am wondering if it would be cost effective to change the rears to Cobras. Weight reduction would be about the only reason to change. How do the size of the pistons compare?
http://www.discbrakesrus.com/make/lincoln/mark.htm