I did soome more searching, and perhaps this will be of some use to you in identifying your motor.

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the way to tell is from the engine suffix code stamped on the ID pad, which is located on a deck surface ledge extending from the front of the block just ahead of the cylinder head on the passenger side. There are too many codes to print here, but the MSA-1 series and Chevrolet By The Numbers both have complete listings.
Their list didn't mention a 427 in '78, and no 366's at all.. but again, it wasn't a complete list. The last years the "Chevrolet By The Numbers" list seems to cover is 70-75.

I'll keep digging..

an idea is only stupid if you think about it rationally.