how to confirm i have sure grip

Today i went to my local savage yard to find a new rearend i found several but was a little unsure which where sure grip and which was limited slip. My question is their i way to tell if a rearend is sure grip without taking everything apart some rearend still have the tire on them i pushed one and one wheel was going forward while the other was going backward. Shouldn't both go forward at the same time.

Yes, both should turn the same direction, mike