He just responded to my email. His radiator fill cap is the highest thing in his cooling system, so he runs a tube from the crossover pipe to extract air from there. The air stops under the cap, using the top of the rad like a swirl pot. No bleed valve needed.
In the car, you need to run the tube either to a pressurised coolant reservoir above the engine (where the air will be trapped), or to a bleed valve.
Clifford Heath.