The Panhard Bar on my '33 Coupe is from Pete & Jakes, and is anchored to a bracket high on the driver's side frame rail and then uses the 9" Ford center section bolts, biased to the passenger side. That makes the bar only about 24-28" long, but I justified that against the limited suspension travel on the rear. If I were doing one from scratch I'd make the Panhard Bar as long as is practical, anchoring on one frame rail to a point very near the opposite frame rail. The longer Panhard Bar minimizes the side travel of the differential as the suspension works. I don't believe it matters which side anchors to the frame for a street car.