B 61 = February 6th, 1961
One interesting thing is that all codes on the spark plug side, I have seen in person and online, always started with B.
I also noticed that the last two digits often simply show the year.
Heads I owned were B 62, B 58 and B 54.
However I also have a 'B 47' and remember seeing a 'B 26' head...
The numbers inside the valve cover do look exactly like the block date codes, don't they ? Who really knows...?
One thing is certain - if the last digit would be a '3' on a 848 head, we know it isn't the casting year.
In any case, the last digit on the spark plug side of my heads always showed the correct year, if the history was known.
And the casting number is what really makes the difference in compression ratio and nickel content, regardless of the year it was cast.
