'73 Duster Budget Barebones Re-Wire!

I think you get what you pay for.
My suggestion is to begin with the design of the circuits best suited to you goals.
Once you understand the basic design that Chrysler used, you can then decide if that's appropriate for your goal and needs.
Opinion on universal wiring harness
There are other design strategies which are better for certain situations and goals.
The factory strategy is simple, although sometimes it was done a little too cheaply (thinner wires or weaker connections).
OTH if you're planning on EFI or some other high demand electric additions, the design needs to be altered.
The thing is that wiring for two or more design strategies can't be mixed.

Then invest in the appropriate wire, connectors and boxes.
Engine compartment wiring should be sized and insulated for hot conditions subject to oil, fuel, and dampness.
Not a good place to use general purpose automotive wire. Marine wire, SXL, and TXL are all good options.
If you are keeping original switches, gages, etc then you will need to have the proper terminations for each of them. If the terminals (metal part crimped to the wire) are not secure to the connector housing (sometimes called insulator), Murphy guarentees some will not make good contact when you push them onto the switches etc.
Sources for Chrysler type wire terminals
You could still go with a kit, but with more background and understanding you'll know if what you are buying will do what you want and hold up over time.
Some sort of open barrel crimper will also be necessary.

You may decide that the easist thing to do is work off the factory harness. Tack it on a large plywood board, strip off the harness tape, cut, splice, replace and remove as needed.
That lets you go one by one, you'll know what you're removing, replacing, changing.
a couple examples here WIRING NIGHTMARE