the o type olds has a 12 bolt cover, you have to take it off and count the ring gear bolts. the diff ratio code are stamped on the right inboard side of the axle housing tube and it dosn't tell you how many bolts are on the ring gear, all that code will tell yu is is weather it is a c type or a o type and the ratio and std or anti spin. you get the code off the axle tube and i can tell you what it is. one way to tell if you have posi is jack the back of the car up so both rear tires are off the ground and turn one tire while turning look under and see if the other is going the oposit way or turning in the same derection, if going the same way you have posi
. i've blown up o type rear ends and have had better luck with c type.