No they are not all posi, If you have a Mopar and you want to upgrade rear ends look for an 8&3/4 rear end out of a Mopar or if you can't find that look into a 9" ford rear. They are a lot more apt to fit.
If you go with Chevy you are going to have to start looking for universal u-joints. One side is bigger diameter than the other side. They can start running into some money. Most of the Ford and Mopars were the same diameter.
