There is a hydraulic porto-power type tool with adapters to push king pins out, and it's much easier, and safer than the hammer and torch routine. I've used various types of jury-rigged adapters involving water pipe, steel plates, and chains with a regular body shop type porto-power to change king pins, but I'm not proud of the fact. The results were successful, but it was not safe or prudent to do it that way.
Jerry
