If you still need to remove the heater core. Here ya go.
1. Disconnect the Temperature cable from temperature blend door and the mounting bracket on top of the heater case.
2. Disconnect the wires from the blower motor resistor and blower motor.
3. Disconnect the heater hoses from the heater core and plug the hoses with suitable 5/8 inch (16mm) plugs.
4. Working under the instrument panel, remove three nuts retaining the left end of the heater case and the right end of the plenum in the dash panel.
5. Remove the two screws attaching the right end of the heater case to the dash panel and remove heater case from vehicle.
6. Remove eleven screws and one bolt and nut attaching the heater housing plate to the heater case and remove the heater housing plate.
7. Remove the heater core and seal from the heater case.
This will get it out. Installation is just as long a process
Once you position the heater core and seal into the case reverse the process above.