You could try torching it. Heat just the headset cup in the hopes that it will expand and the steering column won't. This will smell bad because it will heat the grease inside, so work outdoors. Heat it some, wack it with a hammer some, heat it some more. Beyond that, if you really want to get this bike working, maybe you could hacksaw the fork off and replace it. But I don't think you'll fit the hacksaw on the fork until you first saw through part of the headset.