Well,there is no definitive answer to your question,beacause the rank to mark relation has been fluctuating with each passing year. However,an average (mark my words,AVERAGE) score of about 325 will get you a rank under 1000.
If you are a Keralite,then with a 1k rank you can easily get any branch. If not,then the Fire and Safety branch might elude you. Rest all would be open for you.