Ive worked on so many of these trucks and built so many 318's and 360's I know what each vacuum line looks like and its specific routing. That vacuum line attaches to the intake manifold vacuum port on the right (passenger) side of the intake. The specific vacuum port is about 4 inches in front of the #6/#8 fuel injectors just below the throttle body.
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I edited the pic with some arrows.
The YELLOW ARROW is where the vacuum line attaches to the intake manifold on the right side of the intake manifold.
The RED ARROW is the vacuum port where the line to the cruise control connects. The cruise control line connects here and is routed down the side of the intake manifold for about 10" or so and then goes into the protection sleeve around the throttle cable and then routes in front of the engine over to the left side where the cruise control servo is mounted.
The GREEN ARROW points to the line that goes to the HVAC housing and it is the line that passes through the firewall in the foam gasket for the evaporator. This also connects to the line that goes to the vacuum reservoir underneath the wiper cowl.