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The engine block could have holes in the cylinders. What you need to do is connect the water to the thermostat housing where the water comes from the drive and remove the spark plugs.Find which spark plug holes water runs out of. Seems like you have replaced everything but the engine block. It is possible due to the age of the engine it has rotted out or the engine block froze. Usually when the block freezes the water gets into the oil. If you get water in one cylinder and turn the engine over it will dump water into other cylinders through the exhaust valves and manifolds.
If you have water coming out #7 & 8 these are the rear cylinders of both banks. Connect the water to the exhaust riser on each side turn water on where does the water come out? If water comes out the cylinders you have leaking risers. If no then connect water to the thermostat housing where the inlet water from the drive connects turn water on where does water come out. If water runs out cylinders on both banks of cylinders you have cracked engine block or cylinder heads.