This has come up once or twice before on the differences. The bottom line is that the Cal emmissions one was designed for larger displacement motors then the 289/302. It isn't recommended that you get a cal emmissions unless you are putting it on a car that it was intended for. It is possible that the Cal emmissions one has other internal differences as well.
Someone else who posted in that thread (maybe a year ago now?) may come along, remember and post about it.