Some errors have crept into many places on the engines over the years for various reasons. As we go through running gear repairs we check rod lengths and correct them to print whenever possible so we don't have "custom" and random rod lengths. That is not always possible and occasional compromises are necessary to avoid removing precious material from a rod. As we have to machine the various rods to correct for out of round holes we are slowly getting rod lengths where they belong.
Tramming the drivers goes hand in hand with the rod dimensions. This means having all the driver axles the proper distance apart and in line with the frame center line. The closer all these things are the more smoothly the engine runs and the less wear we see.