Re: 1970 Heater Control Valve vacuum hose routing
It comes out of the firewall via the grommet that has the main vacuum line coming inside the car from the vacuum resovoir tank mounted on the a/c "suitcase".
It is then strapped to the electrical harness that feeds the blower motor/fan resistors etc.
I have the general aftermarket hotwater shut-off valve on mine, but other than this, I reconnected everything factory (except I didn't use the lousy tower clamps on my hose connections!).
See the pic of mine.
-If you don't stand for something, you'll fall for anything.