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Best visual clue to identifying the 5.8 block is the drilled water passage at the 6 o'clock position below each cylinder. This passage flows water to the cylinder head where it is directed between the exhaust valves seats. Also note the slightly larger round holes between the cylinders. These are found on both 5.4 and 5.8 blocks, but in the 5.8 block the passages are drilled, as detailed in the next photo.