Ah ha! “Boys’ Life, the monthly magazine of the Boy Scouts of America, serialised all three books in the trilogy from May 1981 to August 1986. Artist Frank Bolle drew the single page black and white proofs, which were then inked by another person.”
Right when I was in Boy Scouts and got Boys’ Life. So I probably wanted to “see what happened” and got the book from the library. while they were serializing it. Nice – closed the loop on where-the-heck-did-I-hear-the-name “Beanpole” from.