This rear end is in my newly acquired 37 Plymouth 2 door businessman coupe, it's got modern brakes with a Ford/Mopar 4.5 bolt circle pattern, what is it?

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69.5 A12 Bee, first purchased in 1976, car 169 on registry 69 Coronet R/T 440/4 spd 69 Coronet 500 Conv H code 383 4bbl/auto 37 Plymouth PU Find your spot on earth and ride it.