1967 Buick Riviera Radio

In later years, GM was famous for building their cars around the radio, it seems, and you had to take half the car apart to get the radio out. Usually at least three different types of tools were needed to remove the trim plates. On yours, look for a pair of thin nuts around the control shafts. Those have to be removed, and you might need a special thin wall deep socket. There will also be some type of support bracket underneath.