In order to change the heater core you must first remove the entire dash.
You basically have to start at the front of the dash and unhook the instruments from each panel. By the time you get done, everything except the steering column has to be disconnected. In order to get the dash out, tilt the steering wheel to the lowest position.
The most difficult part, besides keeping track of where everything goes, is removing the 3 nuts that hold the heater to the back of the engine compartment. Two of the three nuts are almost impossible to see. It took me two hours just to find and remove these three nuts. One is fairly easy to get to, it's near the heater hose connections. The other two you must get at from underneath. One is above the catalytic converter, the other is below the power steering pump. Look for the threaded studs sticking thru into the engine compartment. They are hard to see and even harder to get to to turn.
Good luck~



