67-69 Barracuda 8.25"

Formula S cars typically had 3.23 gears. Sure Grip is a Mopar "posi". The Sure Grip is stronger and can be added cheap since you just have to set backlash. If you can find one for a 7 1/4. 8 3/4 rears were available in 66 and readily available in 67 through 72.