Do you have the cables?
On my 66 longed the single cable comes out and attaches to the double cable by a simple brake clevises. The double cable is all one cable that runs from the left drum to the right drum in a long U shaped pattern running up the frame rails. You will need to have the additional brake clevises that mount under the cab on both sides to help support it. Then you have two hangers that mount inside the frame rails under the bed.