An adjustable panhard bar is not needed with any of the available springs as long as the wheel offset is correct. The wider the wheel, obviously the closer the clearances will be. The panhard bar swings the rearend in a small arc. Sitting at
rest the panhard bar is at an angle from the horizontal. As the suspension springs are compressed the panhard bar eventually comes to a horizontal position, where it acts as if it is fractionally longer. As the suspension springs are further compressed the bar goes past the horizontal and again acts as if it were fractionally shorter. The movement from sice to side is very small. If this movement causes clearance problems than the clearances are too close to begin with.
Short springs only affect the at rest setting. If the clearance problem is with the inside of the wheel/tire at rest, going to lowering springs will help as it will bring the bar closer to horizontal at rest.

John
V-Performance.com