When cast iron just has to be cleaned the quickest and simplest way is with a cutting torch. A little heat, a quick squirt of oxygen, and repeat until you have done the entire thing. Rub it off with a coarse cloth, oil, then heat, and wipe it out after it cools. Good to go.
My wife has her mother's and my mother's cast iron cookware which make it OLD cast iron, no over seas made junk. She has also added a couple of pieces of Lodge in the last few years which has been good. Nothing, absolutely nothing, can equal cast iron for cooking cornbread.