I read through the Castle Farm link some time ago and have incorporated some ideas in my feeding regime.
Mine get a mix of organic wheat and corn, rolled oats and flaked peas (nor organic but GM free), and meal worms as a treat, and they are doing very well. The peas work as a high protein substitute for soy.
One has to keep in mind that free range birds use provided feed in a very different way than confined birds - when free ranging they have a choice on what they want to eat at which point in the day, and mine certainly have their roaming patterns and do not depend on the feeder station that much. They are fit, healthy and laying well.