VanPelts is wonderful, but easy answer, on top the frame rail near the steering box, sometimes on the left rail mid body, and always on the raised pad on the top of the bell housing. originally, they all matched.
After 90 years, don't count on the transmission serial number being correct for the car. You need to rely on the frame numbers. The one ahead of the firewall should be easy to spot unless your frame was crusty or has a bunch of paint on it.