I found a Pontiac 68 4 pinion posi carrier with 3.36 gears last month. I had it shipped to J D Race and Restoration - Jim Mitschke to have it rebuild. I also shipped him my original rear axle so he can install the posi and set up the 3.36 gears. He installed all new bearings. The posi and rear is all with in spec and will be ready to hit the road soon.
Jim made it so easy to ship the rear axle to him and the cost for all the service and the shipping was very reasonable.