This might help you. FRPP lists a throwout bearing for 79 -'04 Mustangs. Here is the part number
M-7548-A <= clickable.
The bellhousing manufacturers typically use clutch forks that duplicate the OEM offering. If a particular engine was available with a diaphragm style pressure plate and also a Long Style or Borg & Beck style plate they could use a different arm for the diaphragm pressure plate.
Here is a link to the Holley pages for
Clutch Forks <= clickable. A quick visual comparison should tell you which one you need.
Ed