833 OD Decode

"7B175015" is the last part of the VIN of the car the trannywas installed in.

7 is 1977
B is Hamtramck assembly
175015 is the sequential IN of the car.

The "873" painted on the case is the last 3 numbers of the transmission assembly part number, which generally will be specific to a particular model and engine combination.

Mark.