Well you can see there were casting date codes there at one time. The "tell tales" are what look like flat head screw heads (2 sets) along that ground off area. That's where the codes would have been. Unfortunately that's not helpful in confirming the date of block manufacture. The only way to double check the internal specs will be a full tear down and actual measurement of bore, stroke and other internals to know for sure what you have.
The "Captain Bars" is a good indicator along with the 3837012 casting number that it's a 261, just not much chance of confirming dates.
The head date casting code
L 11 1 decodes as December 11th, 1961. Confirmation that the "848" head has the "steam holes" to run on the 261 block is another thing to confirm only through tear down. Best of luck with your engine!
