OK, pistons are standard size (witness std stamped on top), no sleeves, new one piece valves, new fiber cam gear, new adjustable tappets. A couple of cylinder holes still show hash marks from the hone. This has a 5 bearing cam shaft, appears to be re-ground. Per Pluck's paper, Front oil dam is even with the push rod boss, middle dam is low. This, along with the elongated water passage hole places this engine after 3/12/28. Looks to me that the serial number is authentic as far as calendar dates go. If I had to guess, it looks like someone totally rebuilt this block, ran it in a bit, and then stopped using it. I'll try to track down the owner to gain more info.
Frank