Does anyone know what the 18 cast into the block on the opposite side of the water outlet from the casting date means?
I have never seen anything definitive about those numbers cast onto the block forward of the water inlet. What is known, is that they were some kind of mold mark that were likely used to trace defective castings back to the cause of a defect. Molds (exterior and some of the interior molds) as well as the mold patterns were used over and over again. Eventually they wore out and had to be repaired or replaced.