I fitted the GAZ adjustable platform shocks and am very happy with them. I got the black versions from Martin Robey in the UK (Jag specialist, mostly E-type), pre-installed with new aftermarket XJS springs.
They have damping adjustment which isn't ideally suited to the road but good enough:
On the rotary dial, 1 click from softest is...very soft, about the same as totally worn out OEM. You can easily bounce the rear of the car by pushing on the boot.
I have them set at 4-6 clicks from soft, which i'd say is slightly stiffer than OEM but quite comparable and still retains a nice ride. The adjustment range between 1-6 clicks makes quite a lot of difference.
They go all the way up to 20 clicks but anything over 8 or so is what i'd describe as extremely stiff and kindof pointless for road use.

 

Ok sorry. I go away now.