king pin info
Luckily I am swapping out from 6lug to 5 lug and the king pin issue is sorta fresh in my mind.
The two "cups" on top and bottom are king pin bushings. These are supposed to be pressed in. If one has fallen out that is bad, maybe a symptom of another problem. As mentioned by another poster, the retaining bolt secures the king pin in place. Without that you could have a failure since the king pin can come out.
Safest bet is to dissassemble that steering knuckle and replace the crush bearing, bushings and lock pin. A bit of locktite on the end of the threads of the lock pin bolt will keep it from vibrating loose.
The same lock pin design is used on the front of the rear spring shackles of my 59 chevy.
Be mindful that your bushings have to line up with the grease fittings if they are of that nature. Usually you have to puncture the bushings and pry them out. Having them loose is not good. I would definitely check to see if any damage happened to the joint that the king pin is part of... hopefully you got lucky and caught it early.