What's the name of a children's book about a boy who lives on the moon and has to carry around a bowling ball so he doesn't float away has a turtle like pet and was written prior to 1980?

Answer 1

It's the Matthew Looney series by Jerome Beatty, Jr.

Answer 2

The book you are thinking of is likely "The Phantom Tollbooth" by Norton Juster, first published in 1961. It follows the story of a boy named Milo who embarks on a magical journey through a world where he meets many interesting characters, including a pet named Tock who is a "watchdog" (a dog with a large clock in his body, not a turtle).