That is one of these slab sided switches, there are several versions and colors available and also a fog light (rare) that goes right next to it.
https://www.flickr.com/photos/advance-design_parts_co/8129447791/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/8129466604/in/album-72157631868452754/
The switches came with the factory heaters and the dash is punched for their placement. Here is one that is included with a recirculating heater I own (NOS).
https://www.flickr.com/photos/advance-design_parts_co/8129444438/in/album-72157631868452754/
Another NOS heater.
https://www.flickr.com/photos/advance-design_parts_co/8129307001/in/album-72157631868452754/