To expand a little on what Lou has said.
The casting number will identify the block and application for which it was intended. You will also find a casting date which will start with a letter, representing the month the casting was made. A for January, B for February, etc. next will be a day of the month so it can be 1 through 31. Finally there will be a single digit representing the last number of the year it was cast. So 7 for 1937 or 1947, or 1957. You will need to use the features of the engine to narrow down the decade in which it was made. Good luck and come back with/for more information and we will help.
Mike