From the Ford factory, the AM radio by itself does not support the door speakers due to the plugs coming out of the AM radio. AM/FM and AM/8 track would. I agree with others: that the fact that there is now an AM/FM radio indicates a change in doors, or after-factory installation of the stereo harness. If the doors had lights already, then the holes in the door and A pillar readily accepts the stereo/light harness.
I would check the date codes on the doors to see if they match the vehicle: you might be able to rule out door swaps.