To me, the most obvious thing to try is to run Data Rescue 4 on the clone. You'll probably need another external HD, unless I'm missing something about how Data Rescue 4 works.
However, I'm not sure I entirely understand your situation. To summarize, it's fairly apparent you have a bad HD. Let's call it BadHD. You also have an external HD, which we'll call ExternHD. You ran Data Rescue 4 for a month, letting it read and recover data from BadHD and writing it to ExternHD. Is this what happened?
I'm asking because you used the term "disk image" when referring to "cloning", without saying where the "disk image" was located. If it was on the original BadHD, then that was a risky thing to do, since BadHD is, well, bad.
If that's what you did, then I don't see any approach that's clearly better than starting over. The disk image on BadHD is a file on BadHD, and needs to be recovered in order to be useful. I don't know if Data Rescue 4 can be told to recover a particular file (the disk image), and whether that would be certain to take less time than starting the recovery over from scratch.
If you have an external HD (or more than one), then please identify them clearly, and what role they played in the recovery process (if any). A clear description of the exact problem, and what's located on each HD, will go a long way towards useful ideas on what to try next.