How do you remove heater core in 1962 rambler classic?

The heater core is contained in the plastic/fiberglass housing assembly fastened to the engine side of the firewall. Unplug the wires from the fan motor on the firewall and remove the Phillips screws fastening the plastic housing to the firewall. Remove the heater hoses from the core inlet and outlet and tuck them out of the way. You may have to reposition some brake lines and cut a couple of wiring harness plastic ties. You may also have to remove the lines from the fuel pump to the carburetor if they interfere. You may need to temporarily remove the rocker arm cover. Pull the plastic housing away from the firewall and you will see the heater core inside the housing.