The speed tone rings and sensors ARE mounted on the axle ends. They won't fit on an 8 3/4 axle! Thus, the aftermarket TCM and tone ring/sensor mounted on the output shaft of the transmission.
Read through my build thread in the member project section Bro... it is titled B Body Stiffening

I would like to have a look at this Sprinter set up. That engine is a deisel though so i can see you buying an after market ECM,, Modern Muscle sells a 2005 Ram ECM with harness and that is what I used.