Sorry guys - I don't have an answer for you but what you've asked for should be possible. After all Alfresco uses Lucene for indexing/querying content, and since Lucene can index any text and you've got a parser to read from CAD then it should be possible. If there's no further response to this thread then you may have to look at the Alfresco source code to find out how Alfresco invokes parsers & analyzers to index MS Office content, etc.
Good luck