Below are directions:
1980-86 With Air Conditioning
See Figures 2, 3, 4 and 5
Do not discharge the air conditioning system.
Fig. Fig. 2: Exploded view of the heater plenum, 1980-86 with manual A/C
Fig. Fig. 3: Removing the glove compartment liner to gain access to the heater core,
Fig. Fig. 4: Removing the heater core cover retaining screws
Fig. Fig. 5: Removing the heater core cover