First, the correct name for a trac bar (track bar) is Panhard rod.
A Panhard bar is used to prevent side to side movement of the body in relationship to the suspension. This is NOT NECESSARY IN A LEAF SPRING SUSPENSION which is why you will not see them installed on solid axle leaf rear suspensions !
If you are getting excessive body lean/roll on corners you need a stiffer anti-sway/roll bar. If you are getting sway, especially from large vehicles passing in the opposite direction, you need better shock absorbers.