Here are the directions I found for you:
1968-77 Except Air Conditioned Cars
1. Disconnect the negative battery cable.
2. Drain the radiator.
When draining the coolant, keep in mind that cats and dogs are attracted by the 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.
3. Disconnect the heater hoses. Plug the core inlet and outlet.
4. Remove the nuts from the air distributor duct studs on the firewall.
5. On post-1969 models remove the glove box and radio, then the defroster duct-to-distributor duct screw.
6. Pull the defroster duct out of the way, and then pull the distributor duct from the firewall mounting. Remove the resistor wires. Lay the duct on the floor.
7. Remove the core assembly from the distributor duct.
8. Install the core assembly to the distributor duct, the reposition and secure the duct to the firewall mounting. If necessary, use new sealer on the duct flange.
9. On post-1969 models, install the defroster duct-to-distributor duct screw, then install the glove box and radio.
10. Install the nuts to the air distributor duct studs on the firewall.
11. Remove the plugs, then connect the heater hoses to the core tubes.
12. Connect the negative battery cable, then properly refill the engine cooling system and check for leaks.
Friday, November 6th, 2009 AT 9:53 AM