Well, it's been over a year since I started this thread (my first one on Classic Zcar Club!) and I still have this mysterious orphan E-31 engine block with a E-31 head, the old "Nissan 2400 OHC" valve cover, the older SU carbs and all kinds of black braided hoses, which would all point to a 1970 engine, but it has the higher 060039 serial number. As Carl Beck had indicated on this thread, that would reflect an approximate manufacture date of 10/71 or an early 1972 model. But 1972's didn't have E-31 blocks (Series I only), E-31 heads (Series I & II) or the old valve cover (early Series I only). I think that Carl's hunch that the block was misstamped in the factory is probably the most likely scenario. But, no one was really able to come up with a definitve way to translate the engine casting codes. This engine's casting code is "9X04D"....(9=1969, X=?, 04=day, D=December)???