1. How can I put the MFT back in place in the WD drive so that I get all files on that WD drive available?
You can't I'm afraid.
2. Do I need to do something special?
No, see first answer.
3. As a feature of Recuva, shouldn't there be an UNDO capability as I see that a lot of people online do this?
You may have seen a lot of websites advertising software that can unformat a drive, but their claims are bending the truth slightly.
Once you read the guides of these software applications you'll find they instruct the user to scan a drive to recover files, which isn't exactly unformatting them. If an unformat was possible there would be no need to scan for files. An unformat would simply undo the initiall small write process to the bootsectors of the drive. That isn't the case sadly.
Here's an example, and I've removed the name for obvious reasons ...
How to unformat hard drive with XXXXXXX recovery softwareIt is possible to unformat hard drive because format does not erase the data on the hard drive, only the address tables.
The instructions following that statement actually allude to recovering files from a quick formatted drive by scanning. To me, that isn't the "unformat" potential uses think it is.
Now to your problem ... as the data on your drive hasn't actually been deleted you need to go into Recuvas settings and select "Scan for non deleted files" and then scan again. A deep scan would be more thorough, but with a drive that size it would take a long time.
Another option would have been to use partitioning software to scan for and then maybe recover the original partition with all files intact, but I think quick formatting may actually have made that very difficult. If it was my drive, worth a try even if nothing came of it. The initial scan for the partition parameters wouldn't involve any writing to the drive.
Hope that helps, and let me know if you want any further info.