Pete, you know anyone who has a bead blaster or soda blaster? If so, blast it, throw it right in soapy water and clean it. Rinse extra good, dry then put it right on the burner, low heat and mix vegetable oil and some kind of fat, lard etc.. and cure as nessesary. I normally throw my cast pans in the oven on 325 and rub the down while seasoning.
Key thing is to get rid of all the rust and flaking. Then apply multiple thin coats of oil-- as thin as possible or it will flake. With new or stripped pans I alway go at least three coats. Then don't let it get to that state again! When you are done, rinse it off. If something stuck, dump in hot water whilst the pan is still hot and try to get as much scraped off with the spatula as possible. For scrubbing I use kosher salt and just a little bit of water, too much water and it goes from a rubbing paste to salt water and that's not helpful. Never put away a pan wet-- dry it with heat or it may rust. This is usually a good chance to add another coat of oil.
Just as a note, I've gotten cast iron skillets at flea markets and take them home and spray good old fashioned oven cleaner on them, then put in a plastic bag overnight. The next day they are easy to just rinse off and re-season. Make sure you are wearing rubber kitchen gloves when doing this. Had a hole burnt in my forearm from the cleaner, as it is lye based.
After cleaning it, I butter or oil it up and then "stir" a couple flattened coffee filters in oil so they stick. No rust