will rear sway bar help stop side wall rubbing

panhard rod would do it with a little bias toward the side its installed to . Its a bar that goes from the driver side frame to the passenger axle tube or diff cover. It allows the live rear axle up and down movement (with a very small arc deflection toward one side) without side movement. If you can get the panhard mount off the frame and more inline with the axle tube, then the deflection at ride height will be reduced. It can be installed without permanent alteration of the car, sans a few bolt holes in the frame channel. Check this out:

http://www.afcoracing.com/tech_pages/panhard.shtml