If you look at the picture of the kingpin you can see that it is tapered. It can be quite a pain to get it off while saving the Kingpin as the natural tendency is to beat up on the kingpin, which won't work.
You should support the suspention off the spindle (to some extent). This will lift the kingpin against the force of the spring against the lower cont arm (sitting on its wheels would accomplish this). Loosen the lower kingpin bolt numerous threads (do not fully remove for safety), and strike the carrier a sharp blow. By having the nut still safely on the kingpin it will not fly apart when it comes. Once loose the lower control arm can be removed with your frozen part after dealing with the spring.
Bosch Master, ASE Master, L1
33 years MB technician