Borg Warner also made these over drive transmissions and was used in these trucks with the same over drive tail shafts. I think that the Saginaws are not as prevelent as the Borg Warner. Both transmissions will work. If you find a Saganaw you can convert the 4 speed to an over drive although both transmissions need to be Saginaws. The Saginaw overdrive will have a casting of R10Q-1 on it.
Tom
