Well...got it to work. Honestly not sure how, but since I created this thread, I'll post the steps that worked, for the record.

This might be a dumb thing on my part, but the difference between what worked and what didn't was primarily that the contextual menu (right click) options worked, while trying to go through the application gui didn't.

I mounted the disk, right clicked on the volume, and chose "Create Image"

In the version that worked, I made it into chunks of 700MB to fit to cds -- I'm not sure if that's necessary or even relevant, but it's what I did.

Then I swapped out HDDs and right clicked on the first TIB file and chose "restore image"

And it worked.

Of course, not at all remarkable, except that it didn't before.

Anyway, thanks for reading if you did.

Mods, you could close this thread if you like.