If it is frozen from old castor oil, it is likely that the rings are not stuck, and that there is no rust. The castor protects the engine from rust, and though it may cause the piston to freeze in the sleeve, it will free up as soon as it is warm. So even if you free up the engine so that it will turn over, the congealed castor may cause the rings to stick cold, but they will free up as soon as the engine warms up.