...If they are not extremely worn you can fix your bushings (that come in the king pin kit) in the spindles with
"Loctite 660 Quick Metal Retaining Compound, Press Fit Repair" When you use it be sure to line up the grease hole if there is one, and you must install the pin in the bushings to align them, then after it has cured slide pin out and assemble your front end as usual.
With this solution the bushings are no longer free to turn in the spindles and wear them any further. This time all the wear is between the king pin and the bushing, which are simpler/cheaper to replace. I still can't understand why GM used floating bushings to start with... Perhaps easy assembly but sure doesn't pay off in the long run when spindles wear out.
Grigg