Despite severe interference on my DSL line, I'm just about able to report the latest from son.
GetDataBack for NTFS was definitely the tool for the job
it downloaded/installed and indexed 66GB of files in under 12 minutes.
I would be more cautious until I'd actually run the files, but much of the data was viewable without running the associated application - so a major step in the right direction whatever happens.
I'm not at all sure what Spinrite was doing, but four hours into running, it seemed to be swapping every 0 for a 1, and then putting it back.
It does sound as though CHKDSK started without any real input from user. An update invited itself to load - think from MS - and that's when the proverbial hit the fan. Is there a case for hiding CHKDSK from the system?
It's still there in W7. 16kb in system32. Such a tiny file.