At my work... an international garage, we have a portable press. It has a small cylinder maybe 1-1.5 ft. long and a 5 ft. hose to the actual press part to push the king pin down through the bottom which is circular to let it threw. It is an extreme pain in the a&&. I know the big trucks are a little different but it's the same concept. I couldn't tell you where to look for a portable press. The one at the shop is pry over 30 years old. Typically though the pin is beat out with a sledge hammer and a homemade punch (a 4 ft. 1/4 in pipe with a bolt slightly smaller then the pin welded to the end.)
Once the pin is out, the spindle is taken to the bench to remove and insert new bushings as mentioned above. Not sure as to what truck you have, but on my '52 3600 the bushings have to be expanded manually to fit snugly.
