definately your heater box. Just pull out the 2 hoses going to it. may need to apply some force / leverage and there is a high chance of getting coolant splashed everywhere so cover up areas you want to keep dry! once that is done, unplug the orange wire that goes to the blower, this is located on the left hand side and again, will need some force to get it out. Then undo the 6 nuts on the engine bay side, pull out that panel, you will now see into the back of the matrix. Go into the passenger side and unclip the cable clip that sits on the top middle of the heater box. pull out the heater box, should have to tilt slightly upwards as the heater hose inlets are angled, then you can pull it out completely.
Good luck, let me know if you need anything more, i've got all that dissasembled but in rough place in case you have any questions. cheers!
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