Success! The upper and lower damper (shock) bushings have been changed: no more clunk. A couple of thoughts: the aluminum coupling, drilled and tapped for 10m1.5, and with rope attached made the job much easier, and in one case the damper was removed and replaced single-handedly. URO upper bushes came with new nuts, but in one case they stripped well before I even reached for the torque wrench. Fortunately it was the new nuts that stripped, not the studs, and I had not thrown away the original nuts.
Given the sizing problems with the URO lower damper bushes (see separate post), I will have to think carefully before ordering parts again from that quarter.
I found it extremely difficult to manipulate the upper wishbone and damper, and all attempts to wire the brake so as to prevent the item swiveling sideways and placing a strain on the brake hose failed. Anyone who has an idea about how to manage this problem might post accordingly
A final comment on the job: I tried to get smart with the second coil removal, having struggled to get the placement of the compressors exactly - and I do mean exactly - 180 apart and grab enough coils to achieve adequate compression, while also being able to get the damper rod centered in the spring, so as to engage the upper bushing hole, I borrowed a set from Autozone, with the idea of using three compressors at 120. The borrowed items look identical to the Harbor Freight set that I own.

Well, no, bad idea! As stated by Sam in his video, the compressor bolt hex and knuckle- down (towards the smallest diameter of the spring is the only way to get access to the hex at all compressions. Even then the air wrench is only rarely usable; mostly I found myself doing a frustrating 2 or 3 flats at a time with an open-end 3/4 wrench. Even in the 2 x 180 configuration, the ID - the distance between the insides of the opposing knuckles - is barely enough to allow extraction of the damper.
With three compressors, the knuckles collide with each other at the narrow end of the spring, and therefore have to be placed at a much larger spring diameter to even stand a chance. Gotcha: now there aren't enough coils in compression.
I got into a mess experimenting with this, and spent the better part of an afternoon trying to free a compressor nut that had bound against the upper bushing rubber. I'll spare you - and me - the embarrassing details
Bottom line: only two compressors can work, and their placement is critical to success.

 

Yep, spring compressor positioning is indeed crucial. Wayne (cjd777) and I learned that fairly quickly when we replaced the rear shocks and coil spring insulators on my wife's 2006 XK8 back in October 2014. It made replacing the front shocks, poly upper shock mounts, and poly upper control arm bushings a bit easier when we did that job in January 2016....

Hard to tell folks just how to go about it since every set of spring compressors may be a little different in shape and size. We all have to figure it out for ourselves once we dive into the job....