Author doesn't mention that several of those machines with 36-bit words had byte instructions allowing you to point at particular byte (your choice as to width,

Author doesn't mention that several of those machines with 36-bit words had byte instructions allowing you to point at particular byte (your choice as to width, from 1-36 bits wide) and/or to stride through memory byte by byte (so an array of 3-bit fields was as easy to manipulate as any other size). Also the ones I used to program (PDP-6/10/20) had an 18-bit address space, which you may note is a CONS cell. In fact the PDP-6 (first installed in 1964) was designed with LISP in mind and several of its common instructions were LISP primitives (like CAR and CDR).