Knock the king pin buck up the same distance which you originally knocked it down. This will remove the binding tension which the king pin is causing.
Then, without hesitation, hit that threaded end of the lock pin with swift and blinding violence. The pin is softer than the axle and the king pin. It will be driven out without damaging anything. Increase the size of the hammer as needed. If you have a small section of railroad rail or similar, you could have someone hold it against the axle to increase the effectiveness of the hammer blows.
