from KBB faq:
22. My car is more than 21 years old and isn't listed on the site. How do I find its value?
Our Early Model Guide, Collector's Edition does address vehicles older than 21 years going back to 1946, and gives a range of Retail Values from fair to excellent condition. Unfortunately this information is not available via the Internet at this time; the Early Model Car Guide is offered by annual subscription, or you may also order a single book or a certified copy of a particular value in the book. If you would like to place an order, please contact our Customer Service Department at 1-800-258-3266, option 2. If you do not wish to subscribe, this publication can often be found at libraries or credit unions.