Its not clear what you are asking, but if they do not leak, the best bet may be leaving them alone. There are several posts on this board that indicate rust may be the only thing keeping old radiators from leaking.
If you are doing a total renovation of an old house and want to keep everything original, then sand blasting may be the way to go. Plan on replacing all of the radiator gaskets between each section of the radiator.
I would finish by painting with high-temperature engine paint found in auto parts stores. When they say not to paint, they don't want people using laytex wall paint. Also, after several coats of paint, you begin the build up an insulating barrier that prevents the radiator from doing what its suppose to do. Too many coats of paint will reduce the thermal exchange. One or two thin coats of high temperature paint should be plenty.