A panhard bar goes from the frame on one end, to a bracket at the far end of the rear axle. A bar only 1/2 as long as the distance across the frame would be much too short, the tight arc it would trace will cause side to side motion of the rear end. It should be as long as possible and horizontal at rest. That requires a long mount on the frame end which wants to twist the frame. A diagonal brace should be added from the lower end of the frame mount to the frame on the other side. A second brace just above the first from frame rail to frame rail will complete a triangular bracing and prevent frame damage.
i was wondering how much travel there would be. if i put it over the top of pumpkin to the other axle tube if the axis is the same should be able to arch the bar. put axle back in today thought it traveled more than that.. wanting to put bags on back of axle. but if that wont work will have to be in front
If you put airbags on the rear of the axle why not add a stud to the lower mount plate on one side to attach your bar to. Then drop your mount off the opposite frame rail so the bar is horizontal. That should put it behind the pumpkin.