Hello, I was dropping the gas tank off of my 72 Riviera to use its sending unit for my 71 and I noticed the rear end had this tag bolted on the differential end cap. So did I luck out and get a Posi Trac rear end? Was this an option for non GS Rivieras? I remember years and years ago if I jacked it up and spun the tires they would both go the same direction but I've read different opinions about this proving it was Posi or not. Also a side question how do i replace the rear wheel bearings? Do I need to remove the whole axle? There is no bearing cap like on the front wheels? Thank you for any help.