Not sure I'd buy a harness with 20 circuits, labeled wires, proper temp resistant vinyl insulation, complete set of connectors and quick disconnect plugs, with instructions, for less than $400.

I used American Autowire. Certainly not the priciest, not the cheapest either. Worked extremely well for me, roughly $450.

'69 1/2T stepside, Sea Foam Green, 250 L6 w/ 3 on the tree, not an option on it, in the family since new.