So after some refurbishment of the original top spring mounts got both units assembled and refitted. I spoke to soon when I said the near side rear was a doddle to remove, the offside rear fought me! Some muppet had assembled the shock top bolt incorrectly and locked the load spreading washer with a second nut under effectively jamming it in place and hidden by the top bushing... Oh, and the top nut was x-threaded! Ended up having to clamp a mole grip to the shock shaft while I wrestled it off.

There may have been some beeps needed during the afternoon...
The only part I reused was the top spring mount and spacer, after de-rusting they got a coat of Jenolite rust converter. Great stuff and works really fast in 15 mins. Then a couple of coats of grey primer before the black topcoats. In fact, I'm considering giving the rear beam a coating of this stuff as it turns any surface rust black.
As an aside you don't need to use the spring compressors when removing or mounting (I guess you all knew that but this is my first effort!) however they are needed to compress the new spring on fitting to the shock so that the top mount can be fitted correctly in place.