How do you change a heater core in an Isuzu NPR?

Drain out engine coolant. Remove grille. Remove heater core hoses (2, obviously). There are 2 bolts by those hoses you just removed, so you need to pull those. Remove dash panel. The air duct system has several screws that you need to remove. Start pulling the duct system out on the passenger side. On the back side (facing bulkhead) there are 2 screws by the blend door that hold the heater core in place. Remove them and it slides right out. Reverse instructions to re-install. Be sure to top off coolant and run system to check for leaks.