The longevity of the bushing set up surely cannot be denied. Ball Bearing or Torrington being other options of course. Out of 50 or more K engines I've seen or built I would say 90% had no wear, so swapping out, line reaming, etc all uneccesary in many "cases". Surely building any engine you address the weak, worn etc parts, poor designs above all. After seeing so many perfect bushings at teardown I say H-D got that part right. Actually I see more worn stock cam axles! Sounds backwards...Axles are simply made with steel round stock. I forget what high grade steel I bought, but works great. Ends trimmed down would accept KR Ball Bearings. Less friction for the high revving KR, with Ball Crank Bearings also. Ball bearings had a relatively short life, and when they fail it can be catastrophic, compared to a Bushing. In theory, the bushing is just there to give oil molecules a place to hang out.
The bearing vs bushing war continues into the roaring 20s. Ball bearing axles can be softer than Torrington since the bearing just pushes on. Torrington type would surely need precise, harder axles. With the Bushing set up you want to open up a little funnel on the top of the non thrust, case side, bushing. Correct oil. Thick. The K motor is more like a transmission with so many gears! Torrington is an amazing set up, super high loading capabilty, no center point wear like ball. If you have a Minor pit or loss on say a Trans Mainshaft it will not be effect longevity much. Oil retention slot I call them. Think of a log rolling across your lawn over a little mousehole. No effect. Still plenty of support. So bottom line, what would NASA do? Well they have gone back to Bronze Oilite Bushings for infallibility and longevity in many cases. The Launch Vehicle. Biggest truck in the world. After years of bearing maintenaince and failure the axles all ride on bushings with no maintenance except grease gun.