The recovery is still running. Nearly finished stage 4. Just stage 5 to go (checking blank clusters on the disk).The recovery is still happening, nearly 48 hours later. Big disks take a long time, plus I was stupid enough in my haste to run CHKDSK j: /R from within an admin command prompt under the Windows GUI! The process is at least five times faster if run straight from the command line before the GUI starts.
Amazing how much corruption occurred with this single failure! $MFT plus other system files corrupted, many recent files, a number of bad sectors/clusters/blocks. And this is on an Enterprise level HDD. These are designed to run 24/7 in a server environment, and cost roughly 150% of the cost of the 'same' HDD that's not server quality.
Just demonstrates the importance of regular maintenance and backups yet again, folks. Due to other significant life events, I have had to neglect these to some degree for the last 4 years or so.