I'd say you are correct about the H211 block casting date code. That fits with the 0823 engine build date. The serial number format also suggests a '60-'62 range, with the month part of the build date being given as two digits (08) vs. one digit (8). That change was made for '60.
The CON3 is believed to just be a conveyor number. It is of no significance, as is the GM15. 3769716 is the block casting number. Most sites say this is a '58-'62 235 block, as you've found.
