All Cosworths had a rear anti roll bar, but the Sierra mk1 had a longer one that mounts on the outside of the arms, while the mk2 one mounts on the inside of the arms near the brake hose bracket.

If the beam on the 3dr is from a Sapph cossie 2wd it should have the mounts at the brake hose bracket.

If the beam on the Sapph is from a normal Sapph it will not have the brackets, as only the Cosworth and the XR4x4 had them.