I guessed that the Library of Congress might have some old copies of the Cornerstone. I did a search of their catalogs and found a 1976 edition of the Cornerstone and a 1961 edition of the Manual, which was used before the Cornerstone. I'm pretty sure you have to be present to look at a book from the Library of Congress. Since both of you (I think) are far from DC I guess I'll have to pop in soon and satisfy my curiosity for Delta Chi history!
EDIT: I posted link to the two catalog entries but they just redirected to the main site. Here's a link to the catalog search engine:
http://catalog.loc.gov/
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