OK, I have been away from FABO for a few years (health, other projects, life). I am finally going to get back to work on my '66 Formula S, 4-speed. Am installing a 8-3/4 Sure Grip. The Build Sheet says the car came with a Sure Grip, but it had a 7-1/4 open differential when I got it. I am guessing that the original SG was destroyed and an Open was installed in its place. Then it should be back on the road.