Vacuum lines

Don't know if this helps. It's from a 68 service manual for a 273 Valiant.
318 and 340 should be the same.

I don't know if they made changes for the Duster or not. It's the way my 68 Barracuda 318 should be set up with the 3 vacuum hoses.
I don't know what year they started using the vacuum reservoir that would only have 2 vacuum hoses through the fire wall.

If one of the vacuum lines has a hard plastic end that goes to the vacuum source at the engine.
It maybe a totally different setup.
Maybe someone with a 70 Duster with A/C will chime in.



Here's a rough sketch.
View attachment scan0002.jpg