Half the Cars Running on the road today don't have serial Numbers on the Deck Surface because the Block has been Remachined by a Machine Shop. 15 years ago it was considered a Bad Job not to Machine the Deck and knock off the Numbers and nobody cared about matching Numbers. However the Idea was to Machine the Deck in relation to the Crank unlike the Factory's Broaching Job. This would make the Surfaces more Accurate. However if Both the Block were " Decked and the Heads Milled or Angle Milled and nothing was removed from the End Seal area it could be getting Close. My 2 Cents worth. Richard....