The correct tail light for the 1931-39 Chevrolet truck is the SA-140. If you look closely at the bottom of the picture, you can see the rubber grommet that the bulb pushes against inside the housing to create a "lens" for the license plate light. The light is actually shown in the picture upside down. The correct tail light for the 1940-54 Chevrolet truck are all of the tail lights listed and shown. There are several through the years and the correct one for the late 30's car is a tail light similar to the truck tail lights with or without tail light lenses for license plate illumination depending on whether it was a right or left tail light.
The tail light that was introduced as the in the 1940 truck model year has for many years been assumed to be the same tail light that was used as the 1931-39 truck tail light. It was not, but was very similar to the early to mid 30's car tail light in shape, but was actually smaller in size. .
