I'm interested in this project too.
When I was 16, my very first car was a plain Jane 1968 Mustang coupe, 200 cid 6 cylinder. I lived in cold country, and immediately noticed the rear window would fog up. So my first upgrade was adding a rear defogger. I used a cheapo version out of the JC Whitney printed catalog. It was functional, but ever since then I've always thought it would be cool to have a factory one. Very rare. I think I've only seen 1 in person at a car show.