I found an even older reference to impure Lisp; doubt I'm going to do better than this: McCarthy's 1958 paper "An Algebraic Language for the Manipulation of Symbolic Expressions"[0], immediately after introducing our good friend car, says: "For example, statement beginning car (i) = causes a quantity to be computed and stored in the address part of register leaving the rest of the register unchanged."

0: http://www.softwarepreservation.org/projects/LISP/MIT/AIM-00...