Clericuzio (as in Don Domenico from The Last Don) was either Puzo's mother's maiden name or her first husband's name -- I'll have to look it up. His household was similar, to a degree, as the family in The Fortunate Pilgrim.

In The Godfather Papers and Other Confessions, he explains that some of his older siblings kept the surname of Clericuzio, however they had all shortened it to Cleri. (dedicated to Anthony Cleri)

Similar to John Merlyn in the semi-autobiographical Fools Die, Mario wrote a lot of pieces for pulp magazines which, in his words, he considered "schlock" and not "true art". His pen name for his magazine work was Mario Cleri.

Six Graves to Munich was written in chapters in one of those magazines, similar to the way a lot of Charles Dickens' works were originally published. It has recently been re-released in Europe (and I think here in the States too) as a Mario Puzo work "written as Mario Cleri".