The existing bracket is pretty tall and will do nothing for roll center. Just making a point as I don't think you will be auto-crossing the car next weekend. Like Pat said the track bar is not going to work that well on the street, as you have discovered. There is too much leverage on that short bar for it to be affective.
Make the panhard as long as you can. A short panhard bar will move the housing in a quicker arc, cross car, then a long bar. This actually moves the whole rearend side to side as the bar is swinging in it's arc of travel.
Pat and I built this housing for my Astro. Notice the side support going out to the shock/panhard bar mount.
http://images61.fotki.com/v249/photo...MVC010F-vi.jpg
http://images16.fotki.com/v301/photo...MVC011F-vi.jpg