It sounds like your engine builder is looking for an excuse not to finish the job. You should ask if they have done any pressure testing or other diagnosis to determine if the "crack" actually goes all the way to the water jacket or if it's just a cosmetic blemish. I'm going to guess a crack that long is the result of frozen coolant. It usually happens right at the bottom of the water jacket just above the oil gallery that runs the length of the driver's side of the block. As long as you don't run a high pressure radiator cap (4 PSI or less) a crack like that can be patched with "Marine Tex" sealant by grinding the block smooth about an inch or more wide in the area of the crack and applying a layer of the sealant. As it's curing, press a piece of 40 grit sandpaper over the patch to duplicate the surface texture of the crankcase. When the block is painted, the patch will be virtually invisible.
Jerry

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