Got my 340 home

On one side of the block it has the casting #'s that you found and on the other side it should have a date code just below the deck rail casted into the block just as the casting # and it should also have a time code and a D or N and a arrow pointing to one of them. This tells you the day, month, and year that the engine was casted and the clock with the D and N tells you what time it was casted and day or night shift.