Many people call it a Saganaw but it doesn't really matter if it makes them happy. I'll go with my parts supplier, Anaheim Gear, their books call it a Muncie.
There were three 3 speed transmissions available in 57 for cars, the standard SM318, the OD SM319, and the close ratio Corvette version. Trucks had the first two plus a heavy duty Warner non OD unit which has a 9 bolt side cover.
None of the late transmissions will fit your early bellhousing. The Saganaw 4 speed is still 1:1 in 4th gear, so would be no improvement for highway speeds. OD's work great in older trucks, I have installed many of them. None that old, however.
Fred
