How do you read the casting date on big block heads?

On 906 heads made '68-'70, I think it's easy. For example I see under the valve cover is a code attached near the cast part number. For example on a 906 head one might see 11269 which would be November 26, 1969.

I think I have it down for the 452 heads which were made '76-'78. A 452 head might have the numbers 1677. Is that the 167th day of 1977?

On 346 heads which were from '71-'73 I can't figure it out. A 346 head with 2230. I am thinking 223 day of 1970 but I thought the 906 head was 1970. Please help!

You do realize that the model year assembly started in August of the prior year , Engines would have to have been built prior to August for that model year and parts that required casting and then being machined would need to be cast well in advance of the coming year they needed to be used in ...

What's your fixation on 346 and 452 casting dates ?

No fixation. I just have some I'm selling and people are asking about the casting dates.

I had looked around here and on the web and couldn't figure out the '70 date. Didn't even cross my mind it's because they were cast the end of the previous year, not the model year.

thanks!