I am going through the same thing with my '78 Caballero. I have been writing about it in the "what did you do to your gbody today" thread. Just this last weekend I was prepping my future AC dashboard and wiring. My AC dashboard came from an '81 El Camino at the wrecking yard. I happened to find an '81 service manual in the car as a bonus. It has excellent wiring schematics, but the schematics that you can find in a Haynes or Chilton's manual are pretty good too. In fact, the Haynes and Chilton's will cover multiple years and can show you any changes between the '84 and '86. One of the things to also check is the instrument cluster connection if you are swapping to a different cluster. Another thing to check, would be the plug wiring to the vehicle's computer, to be sure that they are the same as your's. With mine this last weekend, I cleaned things up on the backside of the dash, tidying up the wiring loom and identifying the wires that the previous owner cut.
Hope this helps you.