RamAirDave is correct. Additionally you will find the last digit of the year after the julian date. A box build January 15, 1970 would read "015 0". There is usually a small space between the julian date and the year digit.
Check out this box on ebay. Dated 084 0, That translates to March 25, 1970.
http://cgi.ebay.com/ebaymotors/CHEVY-CHE...030312574QQrdZ1
Phil Woj.