Measure either if they fit good and snug. Should be able to push the pin in the axle by hand or light taps with a mallet but will not fall out.
If sloppy in the axle measure the bore to see if metal is available to ream for an oversized kingpin to solve the problem.
If really sloppy enough that oversize kingpin can't be fit you replace the axle.

Pretty sure there is just standard size and one oversize which is likely 0.010" over. Have you checked to see what is available?

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-