posi?

[dinnut]

my main question: do i have a posi/limited slip rear end. i have a stone drive way so spinnign the tires is very easy. today i uh "accidentally" floored. this was after backing up and pulling forward a couple times. went behind the truck and both wheels had spun! usually on the right wheel spins! i might have to try it again later just to see if it does it again! the truck seemed like it was twisting when i held on the throttle for a second. is it possible that only both engage sometimes??? and usually on the right engages. i know the only real way to know is to pull the rear diff cover and find out but too lazy right and know and was just wanting some of yalls input. the previous owner said this rear was swapped in because the other rear end wasnt very highway friendly. and i was going to maybe swap in the rear end out of my 72 which is not a posi and im hoping the 70 has the wider rear now so i dotn have to swap the whole setup, just the axles!