Michael,
Sometimes it's easier to do a task if you chop it into little pieces..it's much less daunting that way. I don't know how much alike your '58 panel harness is to your '55 pickup harness but they are probably close.
I think the best place to start would be in the middle, in the dashboard area. None of this stuff is negotiable, it's pretty well fixed. Get the middle piece situated and lock it down with a few zip ties. Now you should have a basic leg that runs forward and one that runs back toward the rear. Those are the little bits...the middle hunk, the front hunk and the back hunk.
You can make a list that shows all the items that need a wire run to them, things like the alternator, the coil, the temperature sender, the fuel sender, the brake lights. Look the rig over and think of every 'to' location. Now all you need to do is find a 'from' wire. It's a state of mind, you can do it. Your only obstacle might be the differences in the harnesses between those two years. Draw a bunch of pictures and study them, you will do fine.
Stuart
