I once saw a parallel panhard setup that eliminated the arc bind but can't find any pics now. It had a bar attached to both frame rails. The bars then attached to a vertical fulcrum lever that had a center pivot. The center pivot attached to a bung welded on the center of the rear axle cover. As the suspension moves thru it's travel the bars move the fulcrum lever instead of binding up.
Anyone remember seeing this setup and can scrounge up some pics ??
Found it, it's known as a Watt's Link. Here's an illustrative pic.