I think Richard is misunderstanding what Jon is referring to as a diagonal track bar (or link), which is different than a Panhard bar. As mentioned, a diagonal trackbar, used with either a 4-link or ladder bar type suspension, attaches at a front link mount on the frame and the diagonally opposite rear link mount on the axle, to create a triangle within the 4-link or ladder bars.
This page from Art Morrison's site shows both types of bars with a 4-link system. Art says the diagonal bar is for racing setups (drag racing), and the Panhard bar is for street use.
