There is a demand for original two-piece rotors, even if they need to go under spec to be cleaned up. Yes, some classes look for original style rotors and judge accordingly.
The one piece rotors are as Scott described. The bearings and seals were used in many applications up through the late 70s and are widely available. Just make sure that you are getting the smaller hub version. I've come to learn the hard way that many of the big parts houses don't know what they are selling.
Ames has been the most knowledgeable in my experience.
