I don't think there's anything wrong with used axles, especially out of an Aerostar van, and as far as tools are concerned, all you need is a lug wrench to take the wheel off the wreck (if there IS a wheel on it that is), and a small socket to pull the differential cover off. The axle slides right out after you knock the C-Clip off inside the differential.
If you are dead set on buying a set of new axles, they will be custom for your car because it was originally a 4 lug setup, and you should be able to order them from any Mustang oriented speed shop - just look in the yellow pages.
-Matthew