The head date codes are either in the valve cover area or above the exhausts.  I don’t know if this is true across the board, but on the ECZ-C heads I’ve been looking at, heads cast at Detroit have the date codes above the exhaust while heads cast in Cleveland have the date codes located in the valve cover area.

Someone correct me on the date coding if I missed it on this one but I believe it goes something like this.  First number is the year.  Second number is the month, and the letter is the day with the letter ‘I’ being jumped over.  A backwards letter means the alphabet started over.  58H would translate as August 8, 1955.

          The other version, used by GM and Chrysler and most independent  foundries is the Julian date, which is simply the number of the day in total days of that year.

So Jan 1 would be 001, Dec 31 would be either365, or 364 on a leap year.  

           OOPs! you're right, need more coffee here.