Plug-and-Play Wiring Harness

Might be worth buying a new engine bay harness with so many wires in such condition.
I will suggest keeping the original for reference and parts. They roll up and will fit in a med small box. I'm glad I saved mine. New one was great for a 10 years or so but then it needed a few repairs.

A modifications that may be worthwhile depending on your intended use of the car.
Headlight relay harness. While I made mine permanent, no need to do that. It can be made plug and play.
If you're not driving it at night, don't bother. But if you are, then the relays allow a more direct connection from the alternator to the headlights. (The factory wiring was OK with the original 40 / 50 W lamps. Its not really up to the task for anything above that.) Bonus of the relays is that the 9-10 amps for the headlights will not be added to the alternator output wire going through the multiconnector. [You can make a relay harness using a kit from Daniel Stern, or a plug and play by contacting FABO member Crackedback]