Mechanical Changes
Intake and Carburetor: Of course if you are converting from EFI to carb you must have an intake manifold and a carburetor. Just be sure to size the components to match your combination properly. The Building the Perfect Combo article on this website can help.
Fuel System: You will need a new fuel pump and pickup. Do NOT use the existing EFI pump. You can either use an electric low pressure pump designed for a carb (like the Holley red or blue pumps) or go with a mechanical fuel pump. In either case you must replace the fuel pickup on top of the gas tank with a purpose built pickup that does not include an in-tank pump. The Mustang Performance Handbook Vol. 1 includes plans to build your own pickup if you decide not to shell out the $100 that it takes to buy an aftermarket one. If you have a drag car it may be time to upgrade to a fuel cell or modify your existing tank for a bottom sump. At this time I also recommend you go with new fuel line from the tank to the carb. Use 3/8" minimum or larger based on your needs. Remember that many sanctioned race tracks will only allow up to 12" of rubber fuel line so go with aluminum wherever possible, and keep the lines in-between the frame rails for safety. To use a mechanical fuel pump you must change the front timing cover on the engine to one that accepts a bolt-on fuel pump. You may also need a fuel pump eccentric to drive the pump. My '88 motor had one from the factory but I have heard of some roller motors that do not have them.
Ignition: Replace the distributor with one from an '85 manual transmission Mustang. This distributor has a steel gear to be compatible with a roller cam. Also use a Ford Duraspark II ignition box. Follow the Ford Duraspark II Ignition System article on this website to hook it up right. A complete MSD distributor and box could also be used as a step up from the factory stuff.
Brackets & Linkage: Any fox body accelerator linkage will work as long as the car was equipped with a carbureted V8. Look for a '79-'85 V8 Mustang or an '83-'88 V8 T-bird if you go junkyard searching. You will also need the throttle cable bracket attached to the intake manifold and a throttle return spring.
Transmission: This is probably the most critical step of the whole process. If you have a manual transmission you have nothing to worry about. However, if you have an AOD automatic you need a TV (throttle valve) cable. You can purchase this from Lokar Performance (NOTE: this is the same cable that Windsor-Fox Performance carries except $25 cheaper from Lokar direct). Setup is critical so follow the instructions included closely. Setting up the cable wrong will lead to a burned up transmission in very short order.