Once you’ve stripped it out of all its moving components, the engine block seem to be only a lump of metal casted into a certain shape and can be cleaned with whatever you want.
Well, it’s not really like that. Its exterior might look dirty and bulky constructed, but the inside, especially the cylinder area is precisely machined and you cannot go nuts with a wire brush all over the place.
Also, you should not use any water to clean the interior of the cylinders, and if necessary only use oil-based cleaning solutions. Another important part that should not be scraped during cleaning is the the contact surface between the engine block and the cylinder head, which is another fine machined surface and damaging it may result in leaks and even cylinder pressure loss.
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