My guess would be the center finisher with the vent diffuser, then the "funnel" behind it with its flexible ductwork connected to maybe, its own outlet from the heater box, unless GM y'ed from an existing duct.
A body manual would be worth it s weight in gold now.
Somebody else here may have a good suggestion.
There is an electric solenoid bolted to the right front carb, Q-jet, has its own mounting holes, 2 of them, or Holley, bolted to the front left carb bolt, and when A/C compressor clutch comes on, this solenoid energzies to kick up the idle to compensate for load.
Hope this helps,