This site has lots of photos of '58 Overlanders - they should help as far as deciphering the original floor plan:
You might be able to get away w/ removing a "select" number of interior panels to access the wiring that needs to be replaced, however, once you remove a panel and see 50+ year old insulation that most likely was used at some point by rodents of one kind or another (might be why you're having wiring issues), you'll probably slip on the "slippery slope" and decide to remove it all . . .
If you're starting from scratch on the Wiring then you should be able to find lots of good examples to follow by searching here. If you're trying to find something specific then you'll probably get the most help by describing exactly what you're trying to find out.
Good Luck and Post Some Photos.