I believe the right rear and left front (both of the front suspension) and vice versus are interchangeable. And the two types are geometrically the same as well, getting a slightly different shape and a bolt reinforcement around the start of the TwinCam cars.
My car had the early style on one side, and late on the other (yes, I know it was in a front-end accident). I'm buying a matching set of four from another forum member, and can get you the correct one after I have those.