Had a busy weekend, but was able to recheck things today.
Each of the two smaller drives (2TB) have have exactly the same content, which is a subset of the larger drive. Hopefully, the attached image explains what is on the drives. The music and videos folders are the ones I am most interested in recovering.
To best of my recollection, here are the steps I took. Since I don't have any of the drives that unRAID is looking for I got lots of errors when I first started up the box. I assigned the first retired drive to a disk # that wasn't previously in use, #5 I think. I've done the same thing, more or less for the other two drives I've tried, assigning them to an unassigned disk #.The first, and largest/newest drive, I put into the unRAID has several subfolders. Once I copied all the files I wanted to another machine, I pulled that drive out and added the next newest drive, only to discover that the music and videos folders have the exact number of folders and files and total file size as the first drive. I thought was was very suspicious, so I tried a third drive, it too has the exact number of folders and files and total file size as the first drive. It seemed very strange that the two drives had the exact same information on them, and that info was a subset of the info on the larger drive.
I have one retired drive left that I have not tried, but I am wary to install it for fear that I might be writing over the data on the drive. Probably a misplaced fear, but I lost a lot of data and want to recover as much as possible.