I am putting in a 6.0L/4L60E into a 1979 Silverado K10. There are a number of places that do custom stand alone harnesses. Is there one better than another?

I am going to use the truck as an off road, non-emisions vehicle. What do I want to exclude from the harness that would normally be included on a stock harness?

I will have AC an would like to set up an electric fan system. Do any of the custom harness builders make a harness that is the usual 4-plug system plus AC and the fan? What about adding a fuse box for the stand alone harness (to be mounted in the engine compartment)?

What should I be looking for? Is it an unwise option to take a harness from a wrecked '04 Silverado and send it to one of the companies to be customized?

Thanks,
Shane