I'd advise taking to a machine shop and having them press them out. While you MIGHT be able to press them out with a vice, i would say you'll break the vice first, as they're not designed to apply that kind of force, which can be into several tons worth.
Another alternative, if you can gain access to one, would be to use a balljoint press, possibly with some heat. That tool is designed to apply force, and should be able to ush out a kingpin with little trouble.
