Do you mean bushings that have a conical shape when you say ‘properly made’? I do not know what the bushing for a needle point axle should be. Maybe they should be Delran plastic or some form on the ‘slippery’ plastics? And if that is the case, why aren’t they on the market?
The ones I am familiar with that are on the market now are just brass eyelets and not shaped for pointy axles. I conducted my tests using link coupler trucks on a 640 hopper. I had to drill out the hole in the trucks to accept the brass bushing. The SHS steel wheels made more of a difference than the bushings, but not much.
When you think of friction on the axle, it would seem that the link coupler truck would be far superior because there is only the thin edge of the sheet metal in contact with the axle. But as we all know, they have very poor roll-ability. There is obviously more going on here than I know, however this isn’t rocket science and someone should be able to figure it out. The knowhow exists because the newer SHS & AM trucks roll so easily. Now all we have to do is figure a way to retrofit the technology into older trucks.