are you sure its a 289? mavericks never had those stock. to get a AOD in your going to need a custom tranny crossmember. 71gold has a few i believe. as far as the mustang rear it should be a 8.8 and at the very least its going to need to be fitted for the correct spring and shock mount locations assuming its the right width to fit under the car. if not it'll need to be lengthened or shortened accordingly.
:Handshake is it an AOD or an AODE? either way i have a crossmember for it. if you have a 6cyl.now, you will need some mav.only v8 parts. good luck and enjoy... ...Frank...