Referenced on page 82 of The Real Frank Zappa Book.
Zappa once went to lunch in the Tin Angel where Lombardo asked him to be in the band. Zappa asked him what instrument he played? He answered: "Nothing." Zappa replied: "Fine, you're hired." That night Lombardo received a few samba balls and a tambourine. He wasn't paid, but he was allowed to be on stage with the Mothers. Zappa used Lombardo to get people from the audience and bring them on stage.
Later, when the band got to Garrick Theater, Lombardo went to South America to find "The Forbidden City". When Zappa met him again, ten or twelve years later in Sacramento, Lombardo was owner of a pizza store. He claimed he had found the Forbidden City, but had been unable to bring all the juwels to the U.S.