First I removed the glove compartment and passenger side airbag, then the driver side airbag and steering wheel paying special attention not to disturb or spin the clock spring mechanism. Then I removed the center console and several lower panels/walls as well as pillars that are part of the interior trim. Afterwards I removed the instrument cluster that contains the vehicle gauges, speedometer, tachometer, etc followed by the climate control unit and radio. There were many wire connections to disconnect and also the cables between the climate control unit and the vent dampers. Just as I thought I was done, I realized that I had forgotten to lower the steering column. There is a steel ring that holds up the steering column which is part of the dash structure and I discovered that it is easier to detach the bottom of the column near the floor at the universal joint and slide the entire shaft through the ring rather than undo the ring.
Here is a shot of the dash almost ready to be removed from the car.
Here is a shot just after the steering column and entire dash was removed (lots of space to move around).
Below is a shot of the heater unit (left), cooler unit (center), and fan/blower unit (right). The cooler unit (center/black) must first be removed before removing the heater unit (left/white). These units are very easy to remove.
Here is a closer up shot of the heater unit which actually includes the large vent ducts (in black to the left).
Here is a view of things after the cooler unit and heater unit are removed.
On the workbench, the heater core was then removed from the heater unit (accessible from the rear side that faces engine compartment). On the right is the heater unit, to it's left is the vehicle's stock fluid heater core, and at the extreme left is the smaller electric heater core.
Next is the task of building a case/housing that will support the new electric heater core while adapting it to fit into the space of the old fluid heater core. Here is a preliminary rough draft drawing I did on google sketchup.