The Saganaw overdrive transmission was not available until 1966. It can be identified by the 7 bolt side cover. They are very sought after as they are full syncro units. A 62 transmission is a SM319 Muncie with an R10 BW overdrive unit. It can be identified by the 4 bolt side cover. 1st gear is non syncro in the SM319. They work well in most applications.
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