I am delighted to report a substantial improvement in the ride quality of the Duck: some of it may be due to the new 125's and their softish sidewalls, but I strongly suspect it's mostly due to my finally getting ride heights and front bump stop settings closer to factory specs.
It's now a much nicer car to drive on our rubbish Aussie roads.
... a HUGE thank you to Ken and others for helping me through this process!