Help with identifying a motor

Good evening everyone! So this afternoon I started looking at casting numbers for my motor, transmission and rear end (A904 tranny, 741 case 8 3/4). But, when I got to the motor, which I THOUGHT was a 70s 318 LA, the casting number led me to believe the motor was made May 13th, 1955, which I believe makes it a 318 A. Or, I'm reading the casting marks wrong. I'll post pics. Any help would be greatly appreciated!

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