If the Mechanic is familiar with that old of car:Apprx. 3 hours plus parts.Otherwise:Apprx. 4 - 5 hours plus parts.
The heater core is located in the heater case in a diagonal position. It is serviced through an opening in the back plate. Remove the heater core cover and pad and remove the core. Reverse the procedure for installation.
Drain the engine coolant.
Disconnect the two heater hoses from the core tubes.
Remove the glove box for access and remove the right vent air duct assembly (one duct-to-upper cowl mounting screw and three duct-to-blower mounting nuts).
Disconnect the two control cables from the heater case assembly.
Remove the defroster-to-plenum snap clip.
Disconnect the electrical wiring from the resistor assembly.
Remove the heater case assembly (four heater case-to-dash panel mounting stud nuts).
Install in the reverse of above.