Ha ha, I wondered why you were not just asking there. But id almost guess maybe it was a 78 motor or just left over 78 black covers. Ive seen a few 79-s with black but wondered why or when it stopped. Look that PN up on the valve cover sticker.

Would be cool to see the block stamp for kicks. Sorry if I sounded harsh on the E58-s, I do love them (after a cam/exhaust swap).