I have a 1984 M1009 that originally had two antenna mounts at the rear, Phase I. Then about 1986 some brainiac decided to mount them in the center of the body, Phase II. So I also have holes at that point.
I intend to put 4 antenna mounts on the vehicle, but first have to get the mollies to stop spinning so I can remove the bolts. Naturally ALL of the antenna mounts had been removed when I got it.
For you situation, I offer the attached instruction for a Phase I antenna mount. This is the instruction sheet that comes with the mounting kit. You'll notice the backing plates in the illustration. But I don't think they are using the molly bolt system with this installation, at least what I can see from the drawing.