Here's an oddball suggestion, but one that might be considered since you have a limited supply of blocks in your part of the world. We ran highly modified Chrysler hemi engines in tractor pulls with the cooling system passages in the block completely filled with epoxy to reinforce the cylinder walls. I know that would not be an option in your situation, but what about doing a thorough chemical (acid) cleaning of the water jacket, tilting the block toward the cracked area, then pouring a liquid epoxy mix into the water jacket to cover the crack? Lots of these old engines run fairly well with an inch or more of the bottom of the water jacket filled with rust and debris, so losing a small amount of cooling area on one side of an otherwise clean block shouldn't be a major problem.
Jerry
