The book Secret Venice can be bought on line or maybe through Waterstones. The details are The Secret Venice of Corto Maltese. Authors Guido Fuga and Lele Vianello. ISBN 978-88-17-03916-1. Publisher is Rizzoli Lizard.
Also I was wrong about Hugo Pratt he was not an American but born in Rimini in 1927. He lived in Venice for many years and died in 1995.
Euan asked whether Colleoni ever saw the statue of himself on horseback. He never saw it as he left the money for the statue in his will. Whether Verrochio was appointed before Colleoni's death and they discussed it and sketched it out is something I don't know.
Finally there was an error in the presentation. The interior of la Chiesta I Gesuiti was wrong - the picture I showed was the interior of the Santa Maria di Miracoli. The inside of the I Gesuiti is shown in the picture Gallery on this site.