How do I know what rear end I have in my car. It is a 1970 Nova SS with 2.73 gears-posi. I don't know if it is an 8.5 or an 8.2 or what it is. How do you tell and what do you measure. I am getting a set of 3.73 gears for it but don't know what size to order. Had the diff cover off the other day but don't know what to measure to get the correct size. Ive heard that its the ring gear but how do you measure that with all the the spider gears and other stuff in the way?