Yes, according to the manual I have on mounting radios, this bracket is used on the M42 Command Truck.
Now onto the pictures.
Picture #1 is of the mounted radio set (an AN/VRC-10 in this case). This radio is mounted on the passenger side of the bed, you can see the bracket under the troop seat.
Picture #2 is a close up of the same bracket from a lower angle.
Picture #3 is the same mount but viewed from a better angle to show the bolt layout.
Picture #4 is the bolt pattern on the drivers side wheel well for the bracket. According to the manual this is the correct location for mounting an AN/VRC-10 thru AN/VRC-18 radio sets on the drivers side. Also according to the manual this position can change depending on which radio set is being mounted.
If your truck had radios mounted at one time it should have these holes.
Picture #5 is a close up of pic #4.
Hope these pictures have helped show where/how the bracket is used.
When I mounted the radio in my truck I couldn't find these brackets anywhere so I made my own off the print that was supplied in the manual. As you can see they didn't turn out half bad.
This manual I keep speaking of is at work and I don't remember the number off the top of my head. I'm planning on scanning some of the pages and posting them to show more detail, so please be patient.
Kevin