That sequence is exactly how it is stamped? Let me see if I can find my conversion chart.
OK ...
Until I find the correct info, usually,
The FIRST CHARACTER shows the work shift (or shift leader) @ (engine assy plant),
The SECOND CHARACTER the model year,
The THIRD CHARACTER the month of the production year,
The FOURTH CHARACTER the day of the month.
Your THIRD CHARACTER is numeric whereas this position usually uses an alpha character.
If you can find the CASTING DATE CODE on the block, it will help bring all of this together.
I'll get back (hopefully) when I find that other info (Including explanation of X).
DIF = DEARBORN INDUSTRIAL FOUNDRY | CF = CLEVELAND FOUNDRY