Engine stamping numbers

Hello everyone I have a question on the lower stamping numbers above the oil pan. I have included a photo of the stamping I am real curious to know what they stand for.
I bought a 1973 Challenger and the story I got from the widow was when her husband bought the car he wanted a big block but as we all know in 73 no big blocks were offered.
So he bought the car and ordered a 440 6 pack motor from the factory and had the dealership swap the motors.
So I have included 3 pic's 1st lower...


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