I found a letter under the carpet from the original owner. I took some time and tracked her down and contacted her. Very nice lady. She related stories about her daughters growing up in the 69 Firebird, and she is very interested in seeing my car when it is completed.
Unless you can come across something like that, it will be difficult.
Can't a guy still run the VIN through the Secretary of State's "Commercial Look-up Division" for a small fee? That's how I always used to track down previous owners.