1981 z28 3.08 gears is the rear end limited or posi, both were avalible that year but i dont know which models came with which any help ?

See your other thread. We'll need the axle codes.

Posi is limited slip. Power Lock, Sure Grip, Traction Lock, Safety Track, Posi, Positive Traction are all different names for the same thing, limited slip. The '81 could have a standard differential or a limited slip, which would be the Traction Lock in this case.