While not a Rapid Fire lever control this Shimano Revo grip control was easier to find and the cable driven and out board gear indicator is much the same. Shimano made a wide variety of these levers and a few different gear indicators. In time the inboard to the lever body indicator pretty much won over.
You say you have an indicator? Where is it located? If inboard to the lever body then no cable is needed but the body might have still been used which would have also allowed a cable indicator too. Andy