My understanding is those casting numbers don't tell you anything. The 41 you see does not indicate the year block was cast.
This is from VanPelt's web site:
"The foundry would also place what were probably "lot" or "production" numbers in the castings on all blocks. These were usually a small group of letters and numbers cast on the top of the bell housing....right next to the vertical surface of the back of the block. Unfortunately, any records of these numbers are long gone and they provide no clues as to the particulars of any engines."