There was an accessory cab light offered for the GMCs not sure about the chebby. I have never seen a picture, and there is only a part number listed in the accessory catalogue. I believe the panel trucks and suburbans came standard with a dome lamp, but I am not sure if it is the same. It also may have been an option for them.

Some other accessories that were available were armrests, visors (interior and exterior), right side windshield wiper, right side tail light, and right side rear view mirror.

Seatbelts were not an option or factory accessory, and as far as I could tell, neither was an interior rear view mirror.