Another vote for AAW. We have been selling and installing AAW for 22 years in everything from our award winning original Concourse shows cars to high end Pro Touring cars. Back when we started selling AAW, Mike and Frank were a couple guys building harnesses out of the garage. Great guys, great friends, great products. Wiring is never something we have issues or lose points for with AAW.
For the factory replacement stuff they have the original GM blueprints they build from. Depending on your exact options you will spend about $800 for a original replacment plug and play harness set. Or if you have a lot of customs stuff like aftermarket gauges, after market A/C, Electric fans, power accessories like PW, PDL, etc, the Classic Update is a harness built for your car, designed to fit your fuse box, has all the circuits for original connections, and additional circuits for add ons. It is also updates to blade style fuses. you will spend about $500 on a Classic Update and a additional $100 for the factory A/C harness.
If you car is very stock, I suggest the plugand play facory harness because...........it is plug and play!