This should be a straightforward soldering job even if some wires are missing. If you add extra pieces they can be soldered into the original harness with no problem if you do it right, or if you get it done by someone who is good at soldering. Replacing the entire harness would be a tough task with the engine in situ. I had a similar issue committed probably by opossums, the section coming from the MAF was chewed apart just like in your case.
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