Leaf spring suspensions are designed to move up and down vertically with as little lateral movement as they can stand. We all know that there is lateral movement in leaf systems, you cannot get around it.
However, installing a track bar, or more appropriately a Panhard bar, puts a force into the leaf spring suspension that it was not designed to take. By mounting one end of the bar to the frame and the other to the axle, you have now forced the leaf spring suspension to move laterally (like it was not designed to do) with every single oscillation of the rear suspension, because now, the axle end of the Panhard bar along with the axle is travelling in an arc, when it was only designed to travel vertically.
This puts all sorts of forces on leaf spring bushings, brackets and frame mount....wherever you have tied the frame end of the bar that it just was not designed for.
These cars are unibodies with "frames" made outta folded over sheet metal. Over time the frame end of that Panhard bar will likely rip out of the frame where it has been mounted. You can count on leaf spring bushing wear to accelerate as well.
Panhard bars are best suited to link type suspensions where they are designed into the system to begin with.