I don't blame you.
In the past I've used a Linux app called Clonezilla to make images of even corrupted disks, so if anything happens I can go back and try again. And again, if necessary.
You can get it on CD and boot it up on any Windows or Linux computer, and attach some USB storage to hold the clone image.
I'm sure you've thought of everything by now. I think V500's idea to use a pro service is a wise one.
Really, good luck. I hope it all works out.