as far as Heater cores go this is an easy one. Some guys cheat and cut the box open but I don't see the point.
C, K, R & V MODELS
Less A/C
Disconnect battery ground cable, then drain cooling system.
Disconnect heater hoses at core, then plug core tubes to prevent coolant spillage.
Working from engine compartment, remove distributor duct stud attaching nuts.
Remove glove box and door assembly.
Disconnect air-defrost and temperature door cables.
Remove floor outlet, then the defroster duct to heater distributor duct attaching screw.
Remove heater distributor to dash panel attaching screws,
Pull distributor rearward, then disconnect all harnesses that will interfere with distributor removal.
Remove heater distributor from vehicle.
Remove heater core retaining straps, then the heater core.
Reverse procedure to install.
A/C & heater assembly. C, K, R & V models
With A/C
Disconnect battery ground cable, then drain cooling system.
Disconnect heater hoses at core and plug core tubes.
Remove glove box assembly.
Remove screws at center duct to selector duct/instrument panel. Remove center upper and lower ducts.
Disconnect bowden cable at temperature door.
Remove nuts at selector duct studs (projecting through firewall). Remove selector duct to firewall screw.
Draw selector duct assembly rearward so core tubes clear firewall. Lower assembly sufficiently to remove vacuum lines and harness connections.
Remove selector duct assembly. Disconnect core mounting straps and remove core, Fig. 24.
Reverse procedure to install.