It was an option on '66 Shelby's. I had a Pinto with a 302 in it when I was in high school. I put a hone-o-drive in it. With 3.50 gears, I don't remember it being too much of an OD. The speedo cable went back to the unit. It was a pretty interesting setup. It eventually got stuck in low gear, and thats the way it stayed until I sold it.
