Well,
Your story almost exactly matches one of mine. I too bought a 427 standard bore block from a guy who took it out of a Vette. It was a 3935439 casting though.
The Vette was raced and the seller was sure the block was not original to the car. Much like you, I could not find the assembly code anywhere. Then I happened
upon a racing boat guy and he told me that many of the marine engine codes are basically unknown in the real world. BTW, my 427 had mostly L-88 type internals
like the '7115 crank, major domed pistons and 3/8 rods. 7/16 rods weren't available when this engine was assembled. I only wanted to block and struck a deal with
the seller.
I was not able to find any authority on marine racing engines to help me decipher the code. I doubt they exist because the engines were basically crate type applications
and who would really care what was inside once installed. Perhaps the manufacturer of the particular boat ( the engine was in ) might have records, but how would you
trace that since the engine was not in a boat when you got it. Deck it, build it, and run the pants off of it........
BTW, 7/16 rods probably weren't in production use when your engine was assembled either.......
Steve