I just replaced the king pins on my '42 1/2 ton and the above comments about removing the dust caps are correct. They are made of a very soft metal and to replace them you smack the new ones lightly with a hammer right in the center. This deforms them and locks them in place in the shallow detent. You can also stake around the perimeter with a punch.

The tech tip pdf is excellent;
https://www.stovebolt.com/techtips/kingpin.pdf

The tech tip points out that the 1/2 and 3/4 ton trucks have floating bushings. This makes removing the old hardware easier and may not require a press. Try tapping them out with a brass punch. Please note the safety precautions so that the truck does not drop on you!!
Good luck,
Kent

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