I got a used set of fomoco 3.50 gear set at a swap meet for 100$ and a True/Trac from Summit under 500$ and did it myself with a new bearing kit and the Ford manual. Once you get the right pinion shim in there its gravy with no side shims in there and the book in front of you. You do need access to a press to install side bearings and a brass drift.
1965 Fastback-Scat 331, Dart heads, FPA headers, Air Gap intake, 650 Ultra DP, Cobra pan, Lunati VooDoo cam 61003, C-4, 10 inch converter, Reverse manual valve body,Detroit Truetracw/3.50s, subframe connectors.
1968 S-code Torino Fastback= project
1966 A-code Mustang coupe=Basket case not sure what to do with it used some parts for the fastback.