Digit 9&10 in your engine serial number (assuming original engine): vettefacts.com
CQ: Three-speed manual transmission
CR: Three-speed manual transmission with fuel injection
CS: Three-speed manual transmission, high lift camshaft, and fuel injection
CT: Three-speed manual transmission and dual four-barrel carburetors
CU: Three-speed manual transmission, high-lift camshaft and dual four-barrel carburetors
DG: Powerglide automatic transmission
DH: Powerglide automatic transmission and fuel injection
DJ: Powerglide automatic transmission and dual four-barrel carburetors
Cars with optional four-speed manual transmissions used the same engine code suffixes as cars with three-speed manual transmissions. The body number plate is located on the engine side of the cowl. Fisher Body Style Number 59-867 identifies a Corvette.
saginaw 3 speed was the base transmission , april 1957 the four speed was released in option until 1962, 1963 was the introduction of the muncie M20 4 speed.