Check with Dan Holohan and the wetheads at the wall at www.heatinghelp.com. Those guys deal with the steam/boiler heat all the time and can help you with the radiators. If they are in that bad of shape then taking them out one at a time for a good cleaning or blasting may be just what they need. You can check the valves, bleeders, and pop offs as some of them may need replacing. If fact, if they are in that bad of shape, you probably want someone to give your boiler a checkup. Good luck.