As an addendum to this job, I still wasn't satisfied with the handling having replaced the worn idler bushes and adjusted the toe. The car still pulled to the right, steering was rather stiff and numb when driving straight, and small side-to-side rocking motions still seemed to come from the back. all these effects were less pronounced than before, but still detracting from the 'Mercedes' feel.
With the car down on all fours, I rocked the wheels vigorously in various directions by hand. The fronts seemed to have a bit of vrtical play, which I think is strut wear, but I didn't think it was abnormal nor would cause the problem. The left rear wheel could not be moved this way, but the right rear could be rocked considerably fore and aft, when grasped at 9 and 3. Jacked up with the wheel off the ground, I couldn't replicate it, so I put the frame support on a stand, and jacked up the suspension spring support arm. Now there was considerable wobble in the 'track arm', due to a loose mounting locknut at the subframe attachment point. I tightened that to spec, took it for a test drive, and it tracks perfectly now, with no unsettling motions.