727 kickdown lever which one is correct

The correct arm will be the one that matches your throttle travel: butterflies closed to wide open. That lever when mounted on the shaft, when you have the Lokar adjusted correctly, should be gently pushed back just against the kickdown valve in the valve body, but not moving the valve, at closed throttle, and when you press the throttle to wide open that kickdown lever should go all the way back to it's end of travel. I think the Lokar instructions clearly state how it should be adjusted. You may need a different lever with a ratio that matched your chosen carb.