Before I went this far I would try some light oil on the axle ends. In over 45 years in O Scale 2 rail I have never had to convert freight car trucks with ball bearings to get them to roll smoothly. If you attempt to install bearings I hope you have a good drill press in your shop.
Ball bearings may make some sense on models used on a commercial model railroad that see many hour of running time, otherwise proper lubrication should be a sufficient way to get your cars rolling better.
Just my two cents worth.
Joe