Got a line on a 1969 AMX. Apparently most of the body work has been done, but the motor is presently out of the car and it missing the rear axle. What do I need to know when looking for one? Dana 20 I understand, how common is it across the AMC product line for that year? If I can't find one from a AMX/ Javelin will one from something else work? Say an Ambassador or a Matador? Is the track the same? How do I measure it? How can you tell if it's Twin Grip?