Hey there chicken thief.... welcome to the BYC! You did the forum just fine. Couple of thoughts. Scratch grains are not a balanced diet for chickens and are more a treat. You might want to get a basic 16% protein feed and use that as your starting place, then add grains to it. I don't ferment in milk, just plain old water. The thing with protein is the chicken knows how much its body needs and once it's reached that point, it stops eating. So feeding a high protein diet could prove counter productive as the birds will be healthy but will "lean" out. Years ago what folks would do was to feed the birds oats soaked in milk for 2-4 weeks before butchering. The oats have a lower protein/higher fat content and it fills out/ finishes them nicely from what I understand.
You might want to be selective about putting animal protein/products (bloodmeal) in your FF... When animal products start to ferment, the smell will drive you out and bring every fly from miles around in. Whatever you decide to do, let us know what it was and how it worked out for you!
For simply fattening older cock birds, clabbered milk (we use buttermilk) and corn meal or even soaked cracked corn, rice, oatmeal etc are excellent feeds for the purpose of putting a 30 to 45 day heavy bloom on the birds. They are going to be slaughtered anyway but for long term care, more classic FF procedures would certainly pay benefits.