Many of the blocks have been re-bored etc when engines have had to be rebuilt. So they too would not necessarily be original size - albeit not 200cc difference. Your choice is have the wrong engine, or buy the right engine, but still wrong as it's not the original engine block. Or spend your life fretting over the existence, sourcing and purchase of the original block
I think in your shoes, I'd go with making the very best of the wrong block you have. Will it impact value? Quite possibly but that ship has sort of sailed already as unless you find the original block, your resale value is already compromised (at least to those buyers who fret over such things)