I have also heard someone ellode to there being an A or maybe AA stamped somewhere on the bottom around the pan rail oil pump area. I don't know if it was an inside joke or not , bu they treated it like a decoder ring or secret handshake. SHHH others are listening! I have also heard that many but not all are HP2 blocks, but to my knowledge, matching the VIN to a known VIN is the only factual way to know.