This is an Oldie but goodie! It was published by Dial in 1967, illustrated by Mercer Mayor. 175 pages. ISBN: 0803730748
This is the story of three brothers growing up in Adenville, Utah among the Mormon's and other religious groups.
John's older brother had "The Great Brain" that can figure anything out. He is also a mastermind of making money.
This is also historical fiction set in the turn of the century.
John is the youngest of the three. The stories he tells are timeless.
If you are able to find this book, it will be worth the search!