This applies to postwar knuckle coupler trucks with sintered iron truck sides.
When using the eyelets, I have found a lot of axles that were bent, or not running true. In addition, it looks like the axles were cut to length with a "chopper" such that there is an extra edge or lip on one side of the end of the axle. Chucking the axle in a drill and running a file on the side/end of the axle removed the lip and made the axle run better in the truck journal.
Time consuming, but worth it. We all have lots of time these days anyway.