Sometimes, especially for cast iron blocks, threaded holes like these are used by the manufacturer to move the block around from place to place while the engine is getting made. There will usually be a similar hole at the other end of the block, but on the other side. Ovbiously, such lift holes in this kind of a position are only useful for so long until they end up covered by other parts, and then another method must be used.
During manufacturing, the engine can be awkward to deal with, and not just placeable on a flat surface as well as moving it from place to place. For this, a lift-arm of sorts is used and they simply attach it by screwing it to the holes in the block and then move the block around. I guess they figured this was the fastest and cheapest way to go during a certain stage of the process.
Holes such as these are dead ends and lead to nowhere. They will not go through inside the block, as this would allow dirt etc. to fall in. Check the hole and see if it is a solid dead end or not. If it is, it is most likely what I'm talking about here. If it goes through to somewhere, then it is not.
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