1931 Chevrolet Tail light

Here is some information about taillights.  In 1931 the cars only had ONE light on the driver's side.  There was an after-market version which could be mounted on the right side.  Information about that can be found in one of the Service Bulletins.

Measurement was suppose to show hole separation from the center of the left hole.

Yes, all three holes are square.  This accommodates the carriage bolts that mount it to the fender.

Looking at the very bottom.

<click to enlarge drawing>

The left bracket has the license plate holder attached.

The curvature of the mounting bracket is opposite of each other.
I used a grease cap to raise the right bracket so that the base plate would be the same angle as the left side, for the photos.

<click on photos to enlarge them>

Photos taken with my cell phone.  Sorry for the poor resolution.