Heater or valve leak????? How to take it out????

65 and 68s must be different.
there is no need to touch the blower motor.
On a 68 - remove the glove compartment so you have access - remove snap clips - remove outer section of heater box. now you can see the heater core.
Engine compartment - remove hoses and small plate near the hose connections.
Back inside disconnect cable control off the arm of the ??? near the heater core. with some wiggling of the heater core you should be able to remove it,
There may be 2 screws that hold the heater core - can't remember!!
Get new core and reverse. carefull with the new core and especially the tubes as you are re-installing as the connections to the core are not overly solid.