Beware, the model number is not all that needs to match if you will be swapping circuit boards. The drives have different firmware depending on when they were manufactured. You'll need to ensure virtually all ID codes on the drives match up except for the unit-specific serial number in order for them to work together. If you put the wrong board on the wrong drive, it will damage any data already on the disk.
If the files are that critical or valuable, use of a professional recovery service like OnTrack might be advisable.