Does anything light up at all? Headlights, interior when you open the door? Anything? Corvettes (C-3's) are notorious for having ground problems after 40 years. Check the cables- at the battery, the ground at the frame under the battery, and the ground jumper from the right motor mount at the frame to the block. After that, it gets into the fuse links down close to the starter.
Be sure and post some pictures when you drop this on your Dad. There are a bunch of of that are watching this pretty closely for his reaction.