if its in the pinion and you don't know how to shim/ setup a rearend you'll be cheaper to replace the entire unit with a good used piece from pick and pull
thats a really loose converter for that cam
if you have the room go for something mid.600's lift with 300-320 deg of duration on 108 or 106 lobe center
3.73 gears,convert it to mass air, put a set of flows on it, maybe an E or B cam, and some gt-40's or afr 165's, and a tune you'll have plenty of power on tap.
you'll have about the same money as going carb and less hassel
its very easy
the body harness and the engine harness are seperate on mustangs you simply unhook the efi stuff unplugg the computer and remove the harness it all comes in on the passenger side the body harness on the driver side has all the wiring for the lights gauges horns etc... then you need to remove the efi pump from the tank and add an external pump for the carb\
hope this helps