The longer the track bar, the less arc it travels and the less side to side movement of the axle occurs.. See........ longer is better
The 64 axle has a bracket welded to the housing which the track bar mounted
The 69 had a stud pressed in the upper right corner of the casting. I drilled and pressed out the post and only the hole remains. The panhard bar would have been shorter, and I have a 72 bar which would have fit, But I liked the idea of the longer bar , which is a necessity for lowered trucks..
I made it adjustable so the length could be changed if needed to center the axle under the truck.
When you have the front wheel alignment done they should measure the thrust angle of the rear and see how true and square the frame is and if rear axle is mounted square in relationship to the front.
Have you ever followed cars traveling done the road that have been badly wrecked? They now travel a little sideways down the road with the rear tires tracking offset from the path of the front tires. The frame is bent from true square the rear axle is mounted at an angle.