What all do you have to change to put a aod in my 66 fastback that has a c4. I have to pull the tranny and was wondering should i rework it while it is out or put an aod in for the overdrive. I have to replace the shifter fork in the c4 because right now it will not go in to park. The transmission needs to be gone through so i have to make a decision. Original c4 or modern aod???!!!