I personally prefer the aftermarket factory reproductions wiring harnesses. They are specific to the engine type and dash cluster, whether gauges or warning lights. They are "plug-n-play" with the correct connectors, wire colors and gauges. The entire wiring system is available, via 11 different harnesses, so you only have to purchase the harnesses that need attention.

Try:

www.bowtiebits.com
www.lmctrucks.com
www.classicparts.com
www.truckandcarshop.com
www.oldchevytrucks.com

There are many others, but I have personal experience with these...with positive results.