Thanks all. Overhauling the BB is the one basic piece of bicycle mechanics I haven't done (actually I haven't built or trued a wheel yet).
Here is the really dumb question. In order to determine what I need for a replacement, do I need to pull the existing cartridge first?
That would be the safest thing to do. Are you sure it is a cartridge? It wouldn't be unusual to find an adjustable BB in that era Japanese bike.