Saganaw overdrives were not available until 1966 and continued through 69. Completely different unit, full synchro,
special solenoid and governor, fine spline output shaft. Also different shift lever spacing on the side cover due to the
larger 7 bolt side cover.
Fred

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine