Do you know how close the class and race descriptions can be to the D&D text? It would be nice to use basically what they have published.
Simple - sufficiently differnet that no-one would ever confuse one as the other
If you want people to confuse one as the other, you are de facto attempting to break the law.
EDIT: that's a facetious answer, in case it weren't obvious. You've got the entire rule system - making up some new races isn't much to ask, is it? Assuming they won't let you re-use the ones you want to.