Question about rear lights on a stepside bed

[freco]

The picture shows the rear end of my 1969 stepside bed (please note it's placed upside down!). I have the brackets for the rear lights and one has been mounted to illustrate the position. Now, I wonder how the backup lights with clear glass that usually sit below the red rear lights should be mounted? Is there a separate bracket for the backup lights that's mounted using the two screws below the rear light bracket screws (the screw heads that can be seen in the picture) or is the backup light bracket just made as an extension of the rear light bracket, or something else...? I have looked through the assembly instructions for these trucks but couldn't find anything. A picture of a backup light bracket and how it's mounted would be greatly appreciated!