I was under my car and noticed there was a stamped pad on the driverside of the block just under the deck with the number 878N (in a circle) and the number 31 (also in a circle) underneath it. The number 880 is stamped in large numbers upside down (I think) mid block. The prior owner told me the engine was out of an '88 Z28. It does have Vortec heads. Any clues???