Can you believe it? The guys at the local muffler shop had never heard of a "cut out."
When I was a kid, they were one of the most popular accessories used to "hop up" a car. Yes, even Model "A's."
The one I have mounted on "Souper" was given to me by Larry McKinney. We think it came off a WW II stationary engine of some sort. It's the best quality cut out I've ever seen.
Usually the "flapper" valve was operated by a flexible cable running from the cutout to the car's cab. (I've been using a bungee cord to hole the flap "open" or "closed" beacuse I've been unable to find a good place to locate the control knob while maintianing an apprpriate curve to the cable.)
Here's one sold today (2003) by J C Whitney: