Engine decoder help.

[Richs'55]

Sorry for posting engine question here (as it is not original 55 engine) but after 2 hrs on the engine forum, I got 11 looks and no responses.
I thin you guys are just more helpful and knowledgeable about these things.
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Pulled the motor out of the '55 I am working on and got to the engine code and date code (I think).

This is what I found on the drivers side rear of the block.


Am I correct in that this is a 305 from around Oct of '77? The date J777 doesn't seem right to me though. J = Oct.
but doesn't the next 2 numbers supposed to be the day? Never saw a moth with 77 days in it. Last 7 is supposed to be the year, correct?

Correct me if I am wrong , as I am no mechanic. I am just a body man myself.