For a start, the photos show they are DPST, not SPDT. From the diagram, they are double-pole on/off switches. The spade connectors and the 12V suggest they are automotive, as you say.
You could cut off the flange on each side to make them fit in the long, wide slot.I could simply use a jig saw to cut a large opening
A better solution would be to make a punch the correct size. You'll need some serious metal, steel would be preferred to make the punch and the die underneath. Then you can punch holes in formica, masonite, etc.