[notfarnow]

I'm helping a friend swap out the rear end in his 95 Chev half ton this weekend. He bought a used one at a local wrecking yard, and paid an extra $100 for a posi track. He dropped it off in my garage last night, and it looks exactly like his old one (non-posi). I've had trouble with the wrecking yard he used a couple times, and wouldn't be surprised if it's just a regular rear end. What's the easiest way to tell the difference?