The BMW should have independent rear suspension so it would mean lengthening drive shafts, fitting mounting points for the diff, making new hub carriers, finding hubs to fit the carriers, etc, etc...... With regard to the auto box, you may find that you need the abs (sensors at least) for the auto to work properly as it may work on a road speed to engine speed ratio to select the correct gear as it being an 02 model it might not just require engine speed, throttle position and output shaft speed (dependent on manufacturer, both ecu and vehicle, the box will use either gearbox output shaft or wheel speed sensors to determine what gear to select).