Author and playwright Willard Manus is probably best known for his 1966 novel Mott the Hoople. Record producer Guy Stevens read the book while in prison for a drugs offence and later persuaded a newly-signed band to adopt the book's title as their name.
A few years earlier, Manus had written a pair of what would now be called "Young Adult" novels featuring the adventures of skin-diver Bill Bryan. Sea Treasure was published in 1961 and was illustrated by Lee J. Ames.
The Mystery of the Flooded Mine followed in 1964, with illustrations by James Dwyer.
Lee Judah Ames (1921-2011) worked as an advertising artist, fine artist, cartoonist, designer, animation in-betweener, illustrator, and as an artist-in residence at Doubleday. He's best known for his Draw 50... series of instructional books (Draw 50 Dogs, Draw 50 People, Draw 50 Boats etc.)
I haven't been able to find out much about James Dwyer (1898-?) but he appears to have had an extensive career working in book and magazine illustration.