I just recently put an 85 t5spd in my 69 mustang with a 79 engine
All small blocks 289thru351w before 1981 use the 28oz flywheel, 81 and later uses the 50oz. If you are lucky enough to have the flywheel (flexplate) that matches the AOD just simply count the teeth and get one with that ammount of teeth that matches your engine, also you will need the backing plate that matches the AOD trans. The cross member may need to be modified slightly to accept the AOD mount. Also you will have to adapt the TV (Throttle Valve)cable to the carburator linkage. Using a little thought and perseverence that AOD swap will work well! Change the rearend gear to a 3:50 or 3:73 and the performace gains will be tremendous!!!