Not sure what light you have, but beware, not all spotlights mount in the same spot.
I have dual Genuine GM Accessory Guide Spot Lights on my 1956 8400 tow truck. These lights have a rear view mirror recessed into the back side of the light. They mount on the A-pillar between the glass and top of the door using the instructions sheet Bartamos provided the link for.
I have dual (aftermarket but sold by most dealers) Unitity Lights on my 1957 10500 Fire Engine. These lights do not have a mirror. They mount in the cowl just ahead of the door.
The mounting locations for my big trucks will be the same for your little truck.
Spotlights mounted above the windshield was not common on pickup trucks, it was more af a fire/utility company thing. The true roof mount (mounted in the center of the roof) like on my '56 LCF was also a utility company thing.
Send me a PM if you would like pictures. Would also help to see what you have.
You can see my trucks via the link below my signature...Mike's Garage.
Mike B
