Geoffrey Wheeler - found!
I took the no-longer-good phone number and from its area code (260)
figured out that Mr Wheeler had lived in Indiana, in the vicinity of
Fort Wayne. I did a little more searching, and an online source I found
through Anywho told me that he had been employed by Hillbrook Publishing.
Hillbrook, not Millbrook -- I'd misread the title page of the book as
reproduced online. A little more Googling and I ascertained that
Hillbrook Press is, or was, located in Fort Wayne. So I put that in my
citation as the city of publication. Q.E.D.
Thanks to all! The academic world thanks you too.