Feel free to do it anyway you want. I have described the successful method I used and that's what I did. Perhaps the description of fuse block is confusing, the fuse block is actually part of much larger assembly that has numerous electrical connectors plugged into its backside, they are almost impossible to access without unbolting the fuse panel from the cowl and carefully pulling the fuse panel and harness out towards the wheel well. I rarely if ever actually touched the fuse panel, everyone of the wires going into those plugs on the back are numbered. That's what I mean by tracing the wires one by one. If I find a number 23 on a dash board component and is gnawed off I then go searching for #23 generally either on one of these plugs or on occasion the four relays on the wheelwell. Then I hook my multimeter on #23 at the plug and figure out what gnawed wire makes the multimeter beep. I make sure to check that there are zero ohms and then I splice in new wire between the two points. I admit its not fast and easy and if I had to charge someone it would be up in the 50 to 100 hour range. Now that I have notes, that I posted previously I could probably cut my hours substantially especially if I remove the loader as working on the harness with it in the way is a bear.
I looked into installing a different fuse panel, I sure wouldn't want to do it unless I had a spare harness as it is integral to the main block where all the connectors are attached. I would guess that there is some interesting wiring or bus bars between the back of the fuse panel and the row of seven plugs. Not only does the power feed come through these blocks the main wiring between the cab also runs through it.
My feeling is if someone goes the way of custom building a harness from scratch unless they are very persistent I expect they will end up with parts SEE but feel free to prove me wrong
Looks like there may be a secondary market to get a good deal on a SEE bought on impulse with rat damage.