I would say that you definitely should take the old ones apart first to check where the kingpin goes through the axle. If the kingpin is tight in the axle, you do not need over-sized kingpins. You will need standard sized kingpin kit. Most of the time you only really need the bushings, but they don't sell them without the kingpins.
You will need to check the bores in the spindle where the kingpin bushings go to make sure that the spindles aren't worn excessively. You can use your new bushings to see if they wobble in the spindle bores. If they wobble, you will need to find a spindle in better condition.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission