His mix is nothing more than a "fancy" or a high protein scratch grain and not a complete chicken feed.
If you would mix 2 pounds each corn, wheat and milo then change the soybean meal to 4 pounds instead of the 3 1/2 that he said the mix would be about 19.60% protein but it will lack in vitamins, minerals, and I would be willing to bet that the mix will come short in the caloric need of the chicken so they (the chickens) will eat much more of the mix than a well made feed.
How would you remedy the lack of vits/mins?