Should front and rear panhard bars be mounted to the same side of the frame, opposite, or does it matter? thanks-
I'd say in a way yes. With cross steer you'd want the panhard attached same as the pittman to steering arm connection At least on a left hand steering car here in the states, drivers rail to passenger side axle. Mirroring this at the rear axle I'd think would make the car less likely to want to do the twist although subtle as it's jounced about. Furthermore just as important as having them level at ride height (actual pivot points, not "feelgood" or eye appealing longest stretch of a bent or J bar) the front panhard and draglink in a cross steer car are going to be happier the closer they are in length and angle too. Guess you could theoretically have both panhard and drag link at an angle at ride height and not see much bump steer if they paralleled each other even though the frame is getting jarred a bit in bumps.
My panhards were fixed opposite of each other front and rear and never noticed an issue. It handled really well. 32 frame, i beam front, 700 hp 4 speed car which was driven hard. Now I am sure there is there some formula or theory that says dont do it. That is the way mine ended up when I built it.