Most of them are near the rivet heads for the fulcrum.
I have seen later ones though (1970) that are on the opposite side nearer the starter.
They follow the same pattern as the block. First character, last digit of year. Second character, letter of the alphabet for the month. Third character, day of the month.
I'm looking for a 7E20 to 31. I haven't even seen a first half of '67 yet. Later half of '67, yes.
Some are speculating that they are cast in batches, particularly these for the 11.5" clutches since they were much smaller production applications then the small block bells were, BUT that is still speculation and you know what happens when you assume?