First of all, get ready to throw up! I've had castor oil; my grandma was a big believer in it if you felt a cold or a tummy bug coming on. Probably because the castor oil is so nasty it will send anything short of AIDS running for the hills. If you don't throw up, you'll get a case of the back door trots like you've never had before in your life.
Secondly, if your uterus is closed and the baby hasn't turned with his head pointing down, you're nowhere near ready to give birth. Let that baby stay in the oven two or three more weeks before you even think about doing anything to induce labor. What if you took castor oil and gave birth, and then the baby's lungs weren't developed all the way and he had to spend time in an incubator? Not fun. Patience, Mama, patience.