The numbers are all on the right side of the block. The engine number is STAMPED INTO the ledge on the right side to the rear of the distributor. Usually necessary to scrape of paint and dirt to see it. In 1941 the number for a 1'2 ton would begin with an AK or AE....All 1941's started with an A, the letter after it was to identify the size truck the engine was to be installed in. The numbers following the letters will be between 1001 and 1163729.
There is also a casting number on the lower right side. These will be raised nombers and easier to see The 1941 216 casting number was 839400. Some of the other raised numbers will give a clue as to the date it was cast. The 1941 engine (head) used the small 8MM thread spark plugs.