Based off of looking at rebuilt ones, you are looking at a 7.3 specific 4x4 4r100. I'm not sure if the vans are different though I'd be surprised if they were.
A used one will probably be your best bet. Try car-part.com and see what comes up. Try to avoid a 2001 if possible, they are known for failure due to a design change of a diode
A used one will probably be your best bet. Try car-part.com and see what comes up. Try to avoid a 2001 if possible, they are known for failure due to a design change of a diode