In case you're still intrested...
This is the front of my 63 overlander. Notice the two black knobs (dots) on the bottom left of the overhead. That is where my am radio is mounted. It is an airstream model built by a motorolla. It has 1 speaker mounted in the inside of the overhead facing up. There are 3 holes bored in the top for the sound to travel. It looks like an antenna plug at the end of that black wire in your photo. It seems like you would need a square hole to mount a car type radio, but yours could've been a diffrent type. (Story of my life....square peg...round hole).
This is the front of the radio. (Paint job courtesy of the P O. P U).
Some days you're the windshield,
Some days you're the bug!
"Life's a garden, dig it" Joe Dirt