Chris, when I was looking for an SBC long block core to use as the starting point for building a street rod engine, the best (least expensive by far, most abundant cores) source turned out to be Chevy and GMC dealers who had installed "rebuilt" engines in customer cars and trucks.
Like you, I wanted to be able to ID the cores quickly and easily from cast and stamped numbers. That proved to not be possible to do with certainty in many cases.
Fortunately, the dealers were very accommodating and let me pull the pans from the cores to check the number of main cap bolts, bore size and condition and size of crankshaft bearing journals. All they asked was that I reassemble what I disassembled.
You may have to do the same thing to know with certainty what you have there.
