Gary,

You are most likely missing the Ranco valve and control rod shown in these pictures. One shows all the parts and pieces another shows the hose routing.
https://www.flickr.com/photos/advance-design_parts_co/8129313579/in/set-72157631868452754
https://www.flickr.com/photos/advance-design_parts_co/8129334838/in/set-72157631868452754
I run with my heater off and Chevrolet actually offered valves to do this as an accessory so you are fine to close it off.
https://www.flickr.com/photos/advance-design_parts_co/8377101217/in/set-72157631868452754
I run mine shut-off with a custom set of valves I made.
https://www.flickr.com/photos/advance-design_parts_co/8129182239/in/set-72157631867396207

KMAC