There are lots of threads and write ups on this that give you the year & make of donor vehicles, new m/c size and booster and all the fittings to make your brakes work front and back. Search
See http://home.comcast.net/~mjbobbitt/mustang/page1.html for the best and cheapest brake upgrades and 5 lug swaps. The site doesn't sell anything but some fittings, but the tech notes are great. It tells you what junkyard or remanufactured parts to use to upgrade your brakes. It has almost everything you could want to know about Mustang brakes on it.