Papa (or Mr. Disco), the main problem in rewiring is getting yourself under the dashboard. If you can manage that, you have much of the fight already won and with such a simple wiring scheme as the AD truck, I'd think a weekend might be plenty of time. The AD truck compared to one of today's vehicles is like comparing a see-saw to the Space Shuttle. If you get the proper firewall grommets, that can and will make your chore easier also. Personally I don't like wires that are spliced. Even if you splice them correctly, a continuous wire from start to end is best in my view. You might find some of those wires under your dash were added by previous owners and you might be able to do away with some of that wiring clutter.
I started studying electronics in 1957. Obviously, tremendous changes have occurred, but electrons are the same. The man who taught me said "It is a very good thing electrons are invisible. If you could see them constantly flying through walls, windows, concrete blocks, people, dogs and things you would be too scared to get out of your bed every morning."
