I think the issue of a Pan Hard rod arcing the axle left and right is a mute point for a suspension with not a lot of travel (unlike say an off road vehicle). Obviously a watts linkage does not arc but I think the arc for most cars is so small it is not an issue.
I have an old MGB with an engine conversion. It is a pretty spunky car. The problem with MG's is the leaf springs are past their parabolic arch. When you hit a bump they do not do much at first then all of the sudden play catch up. Lousy lousy setup.
I removed a couple leaf springs, added a coil over and threw in a panhard rod. The panhard rod was also added because I went to slightly larger tires and the rubber is about 1/4" from the fenders on both sides.
If there was much arcing at all I would raze a fender but there just isn't. It does exactly as I ask: