While STILL trying to get my '68 327 clean enough for new paint, I happened to notice today the markings on the block (with the images flipped over) look like letters and numbers.
And while cleaning other spots, I found more of the blue paint I asked about before.
Looks like the letters H J. (pass side of the block)
This looks like number 4, then underneight the numbers 29. (driver side of the block, at the very front)
This looks like it says M F to me? (driver side of the block, farther back)