Overdrive transmissions were offered by Chevy in cars and light duty trucks beginning in 1955. They use the same case as the standard 3 speed Muncie with the exception of having a hole drilled in the housing to incorporate the reverse lock out/engagement lever. The overdrive portion and the adaptor plate were provided by Borg Warner and are specific to each manufacturer.
Generally, most of the internal components interchange with other R10 units. IE: Planetary, sun gear, ring gear, roller clutch, blocker ring, etc. The standard 3 speed is referred to as a SM318, the overdrive is a SM319 for the early years. The later unit, a Saganaw full syncro unit is a SM326 - R10Q, 1966-69.
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