These are interesting carbs. I used one a few years ago on my 260 small block after modifications to remove the governor linkage and adapt for car use.
They have power valves in both metering blocks and I think they had the idle circuit on the secondaries.
Mine was a C3TE-9510-C from a 477. The flow rating on that one is only 370 cfm, great for small engines. I removed a bigger Autolite 4100 carb from the 260 to install this SD Holley, and the throttle response and power in the range I used on the street was much better.
The carb is pretty heavy since it has a cast iron base.
I think the two of those would be great on a 2 x 4 intake.
Unfortunately, they don't have much value since most people would have trouble adapting them to use in a car or light duty truck, and most people are in the "bigger is better" frame of mind.
I got mine free from a truck that was being scrapped, and picked up a clean nice looking 1970s version of the same thing for a few bucks at a swap meet a little later.