Who knows what went before.? Whilst the balls might sit snuggly in the cups the cup register diameters may have been changed so check that the cups locate and hold position. It is quite common in engineering to have pairs of cups etc with different diameters on the pairs as the cups stay fixed in one part but free to rotate in the other. It follows therefore that a previous owner may have altered diameters to suit standard thrust races and away from what should be there. Some sizes are not now readily available and cheaper substitutes are looked for. I am a Scott novice but have been selling and modifying bearings for a few decades.