Pontiac heads have their casting codes cast on to the center exhaust ports. Starting in 1965 they were a two or three digit code.
The date code is a 3 or 4 digit code. The first digit will be a letter.
Followed by a 1 or 2 digit number for the day of the month. The last digit will be the year. The date code is usually cast lust below the valve cover or under the valve cover.