That sounds like it - Mystery Motor. The casting date was something-63. I know that I'd seen a pic or something of them before - - musta been the Hot Rodding Chevy's book that you mentioned.
The motor itself was at a facility that has been commissioned to put together a COMPLETE, and comprehensive engine display history for all GM engines EVER produced.
Talk about a MASSIVE undertaking. I saw a Stage 1 Buick motor in pieces, the Mystery Motor going together on a stand, a 396-something waiting for attention, etc. etc. etc. It was simply dazzling to see ........
