Stop in for a cup of coffee
well, the wires going to the tailights are chewed up, guessing from mice. and the engine harness has been hacked up to put in that electronic ignition conversion plus some of the wires such as to the voltage regulator and the alternator, the insulation has dry rotted and is cracked. it actually flakes off in some areas. I'd just feel more comfortable replacing all that. Especially given the melted harness under the dash. Not worth the entire car to save a few hours and dollars.
Engine compartment dry rotted insulation - I get it - that's legit.
But if this is the kits you're looking at, you've got a major project. Using a kit like that is not quite reinventing the wheel, but its close.
It's still generic. Chevy, Ford, Chrysler are not the same. Ford used a 4 wire voltage regulator. Their starter solenoid was sperate from the starter. Few Chevy had full instrumentation like was standard on most Chryslers. etc etc.
Your going to have to figure all that out,
you have figure out the hook up connectors,
you have to rework/modify/change the firewall pass through connections.
presumably you must remove the old and mount the new fusebox.
You'll still need a good crimper, and wire stripper.
I just don't see what this gets a person who isn't very familiar with circuits.
Back to my first suggestion. Copy the factory. Between the Factory Service diagram and the orignal harness, you'll have the wire size, color, length, routing, along with the terminals and connectors.
The only thing that will be a minor PIA is factory colors in relatively small quantities.
just my honest opinion.