At this point Gary, what I have is only heresay and I do not want to start false rumors but I will say that I am currently working on a proposal to a very senior executive at GM about a different approach to finding possible information. I have never worked for GM in any way but I do have someone's ear.
I would like to point out that Chevrolet provides documentation for 1977 and newer cars see link attached. http://www.camaros.net/vis/
BTW I have use this service for my 81 Z. We have heard all sorts of reasons why the prior years haven't been released from lawsuits, floods and fires. The bottom line is if they existed they would have been released, the truth is the records have not existed for years.