As Jim said, body unit number should be sequential by build date in each plant, each model year.

Build date and VIN are by SERIES. Convertible numbers will not fit in the coupe sequence. Deluxe interior numbers will not fit in the standard interior sequence. I have enough information to approximate build dates for '67 generally within 2 weeks. Anyone wishing to contribute more data will allow me to provide a verifier as to whether the body tag corresponds to the VIN for '68 and '69, and will make '67 even more accurate.

http://thefirstgensite.com/library/dbase1.htm