['68OrangeSunshine]

I have one hole in the center of the cab roof of my '68 C/10 Stepside. It was a California truck. I believe it may have originally belonged to CalTrans or Southern Pacific Railroad.
The hole is about 1/2" i.d. and is covered by a black rubber grommet that I have never messed with. It doesn't leak. Probably for a VHF/UHF stubby whip. There are old screw holes where coax cable retainers ran across the cab cieling and down the passenger side B Pillar.
No AM radio, no power accessories, manual steering, 4-Speed SM465, 292 L6, 17.5 x 5.25 Rims and West Coast Jr mirrors are clues to its origin.

The comm radio mods were not factory, possibly done at the dealer level, but more likely a specialist communications subcontractor was involved, unless a big outfit had their own Radio Shop.