I had the IPD sway bars front and rear on my 544.
Put the front bar on my 210 before I sold the 544.
Here is what I observed and what I would recommend.

The 544 was like a bucking bronk, I could feel every night crawler it rolled over.

Investigation, pondering and trial showed the following:
The panhard rod limits the lateral movement of the rear end and keeps the body from falling off the springs. Of course, when the body loads the springs going over a bump, the panhard rod rotates and because it's a diagonal link between the body and the axle this action actually forces a slight lateral motion even when the whole car is going straight down the road.

Now look at what happens when you add the sway rod:
Although rotation about the axis of the bar is possible, (whole idea of the torsion bar), a rigid plane is created beteen the four mounting points (two on the axle and two on the body) which no longer allows lateral movement of the body relative to the axle.

Now that lateral movement of the body is restricted by the sway bar, the panhard rod can no longer rotate through its arc, and the vertical movement of the body relative to the axle is resticted to the point where the rear of the car has become one rigid system, making springs and shocks useless in damping variations in the road surface.

Therefore, if you install the sway bar, and you still want a sprung rear end, remove the panhard rod.