The Borg Warner overdrives only fit a 3 speed. I am in the process of installing a 3 speed with overdrive that must have come out of a pickup because it has a U-joint instead of a slip joint. Its going into a 50 GMC 3/4 ton with a 302 and the original 4.56 gears. I will have a short drive shaft with a center bearing made and use the original rear drive shaft. T89 Warner overdrives were available as a heavy duty option but they are very rare. Most including mine have the Chev front section with the Warner OD behind it. If you require the deep first gear of a 4 speed, you might look for a 5 speed with 5th over. They are hard to find too.