IMO you should not make a blanket statement of "numbers matching", and will always need to describe the block as being "date correct and believed to be original/born with", since there is no number left to match. Best to be up front than have someone later discover the partial VIN missing and start to question the rest of the car's integrity. Also, Iíve seen a MU block with casting dates close to yours that was assembled, as I recall, on Aug 19th, so to me the October 7th engine assembly date stamp raises my eyebrow. Iím not sure it would sit around that long before assembly, but I am not familiar with the inventory methods at engine plants. Also, if it was decked one would think the engine assembly stamp would also be gone. Why would they remove the partial and not the assembly date? As already mentioned, post up some pics.
There are ways to try and pull the old number back up, using chemicals or special instruments. Do an advanced search at the above left section and you should find old threads. Might be worth a try.
FWIW, the engine I mention above was from an 11B car. Seems the inventory control on L48s at the assembly plant must have been FIFO, with some stuck back in the corners and waiting awhile before getting pulled for assembly.