Take notice of the line leading from the water pump going to the heater core, and the line coming from the heater core and going to the water pump. They are usually two different sizes. So you will need an adapater in the middle to fit the two lines together. Pull the lines off the heater core and connect them. This will bypass the heater core all together. So you will get no more heat from it if you do this.
Not sure if you drive the car in colder weather. If so I would recommend what I am doin on my 1969. I and going to add in a bypass line with some valves between the heater core and water pump. That way in the warmer weather I can bypass the heat as I too have lost control of the temperature controls and it just blows heat from the vents. However this will also let me open it back up so that in colder weather I can have heat again for when I want to drive the car.
