Depending on your goals, the Mark VIII upgrade may be an option if you get the parts cheap.
However, bolting on 99-2004 Mustang v6/v8 (non-cobra) dual piston aluminum calipers and using your stock size rotors will outperform the larger mark VIII upgrade due to increased clamping force, and better heat dissipation. Plus, since its from a mustang, you have a candy store full of brake pad choices. Even though the rotor is smaller, it will perform better.
Most junkyards will charge you the same price for a mark VII caliper and bracket, as they will a mustang caliper and bracket.
Either way you need 93+ spindles.
From experience, the 99-04 mustang v6/v8 (non cobra) brakes on stock sized rotors not only outperform the mark VIII option, but give you a much better brake pedal feel. Much more modulated and controllable due to the larger volume of a dual piston caliper. Gets even better with stainless brake lines.
I've had just about every combination of brakes on my SC.. Currently 13" brembos and dual piston mach 1 calipers.
Hope this helps,
Jeramie