I've been wondering that as well. There's a bearing supply house here in town that I think could cross them over. I have a set of the ball bearings from a 1953 3100 that they might be able to get dimensions from. I just haven't had the inclination to do that, as the bearings on my truck are doing OK. I think part of the issue is the inner bearing has an extended portion where the grease seal runs. It might be possible to replace that with a simple spacer of the right dimensions.
