Darren,
The group of markings in your photo above are the marks that the foundry use to enable them to keep track of which blocks were cast on particular days or from a particular batch of iron. If there are problems they can then isolate affected batches.
The number 3738307 is the drawing number of the casting. The finished block would have a part number depending on the exact way it was machined. Thus a block with blank pads for an accessory would have a different part number in the factory to one with them drilled and tapped but that number would not be stamped into the block usually. Notice that the actual engine number is stamped into the machined pad but the casting and production batch numbers are cast into the block, not stamped. You can't stamp a raised number ! The casting number is only changed if the un-machined casting changes, so extra features would get a new number whether it was an extra pad for a bracket or bigger bores or different water ways.
David
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