O.K., panhard bar. The shorter the bar is, the more it will want to yank the diff left to right as the diff moves through suspension movement and the more bind you will get in the mounting points of your 4-link. Make the bar as long as is humanly possible within the confines of packaging it to fit into the truck. Construct a bracket that welds to the diff and anchors the bar very close to the backing plate at the wheel. On the other end, construct a bracket that welds to the frame and positions the end of the bar as close as possible to the backing plate. At ride height, the mounting points of the bar left to right need to be level. Note that I didn't say the bar needs to be level, but that the mounting points of the bar need to be level. You can twist or bend the bar into a pretzel to clear other components, so long as the bubble on your level is at neutral when placed on the MOUNTING POINTS of the bar at the frame and diff. It will make little difference whether one or the other of the mounting points is a little ahead or behind the other to miss other components on the truck, so long as you don't carry it to extremes. Let me say this again, MAKE THE BAR AS LONG AS HUMANLY POSSIBLE.