It would be best that a qualified mechanic performed replacement of heater core as Special tools and Equipment are needed. Air Conditioning system needs to be Discharged using approved refrigerant recovery/recycling Equipment to remove Heater/ Evaporator Case. Air Bag system needs to be Disable to remove Dash assembly.
I have replaced the heater core in my car. The pain in the butt about it is taking the dash out. Then I came upon a youtube vid (after dong mine) that shows an easier way. There is a little hooklike thing under the dash right near the core that's connected to the dash and I remember seeing it and thinking hmmmm if that was out of the way.... Anyway this guy on the youtube vid said that its only purpose is to help line up the dash for installation at the factory and you can just cut it off and get the core out w/out taking the damn dash out. Haven t tried it but I will next time. Hope it works for someone.