The heater core come out from inside the vehicle:
See Figures 1 through 9
CAUTION When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.
Fig. Fig. 1: Disengage the heater hose locking tabs ...
Fig. Fig. 2: ... then disconnect the hose from the heater core
Fig. Fig. 3: Loosen the heater core trim panel retaining screws
Fig. Fig. 4: Remove the panel and set it aside
Fig. Fig. 5: Unfasten the heater core cover retainers
Fig. Fig. 6: Remove the cover to gain access to the heater core
Fig. Fig. 7: Loosen the heater core retainers ...
Fig. Fig. 8: ... and, if necessary, remove the bracket from the case
Fig. Fig. 9: Remove the heater core and seal from its housing
Once you remove the hoses, then remove the covers, remove the retainers and brackets holding heater core in place inside the heater unit housing, and then the heater core will pull out without having to remove the whole housing unit