Lehrer's historical note places the song after his arrival in Cambridge in 1943. Its station names belong to that period, not to a current transit guide. The sheet identifies Theodore Morse's M-O-T-H-E-R as the tune and Howard Johnson as that song's original lyricist; the eight replacement lines here are Lehrer's. A source footnote explains the final acronym as a throat-clearing and spitting sound.
H is for my Alma Mater, Harvard
C is Central, next stop on the line
K is for the kozy Kendall station
C is Charles, that overlooks the brine
P is Park Street, busy Boston center
W is Washington, you see
Put them all together, they spell “HCKC-PW”
Which is just about what Boston means to me.