After posting, I went and looked at the valves again (not zenith carb) and remembered that cars including A's ran a service wire to a choke plate, etc. For the ball valve in the photo , which seals well with modern fuels, I drilled a hole in the valve lever and am going to run a stiff 3/32 or 1/8" wire thru a tiny grommet in the firewall. For longer period stops,can open hood and shut off both valves.
Sorry, the Barn right now won't allow photo up load? The small ball valve is attached directly to the horiz. stock brass valve port and then receives the stock gas line ferrule.
Update: valves photo attached with hole in ball valve lever. stiff wire run thru firewall