With that out of the way, disconnect the A/C line spring locks (special tool required), remove the entire dashboard a piece at a time, unbolt the HVAC box from the engine compartment side of the firewall (which involves removing a half dozen things from the engine compartment first), pry open the HVAC box, remove the heater core. Installation is the reverse of removal.
If you already know what you're doing, you're looking at around 8 solid hours. If you don't, a couple days.
