You might want to start an approach on familysearch.org using the census data and see if you can find Vallelunga living in the same towns as Madeline Guzzo - as families often settled close to each other. I don't know if the census below is your grandmother - living in San Jose in 1920? - If it is, you might want to search Vallelunga b. Italy, living in San Jose in 1920.
You can also look at names of spouses in the census that were born in the CA/US and are spouses to Italian born Vallelunga men! Then you can take the names of the couples and est birth dates and and look for US/CA marriage records which might have details as to parent names and look for additional matches that way. And you can guess an approximate marriage year by the age of the oldest child.
During the WWI war years, there are also some Draft Registrations of Vallelunga males, b. Italy with more specific details such as city/town of birth and street addresses that give more clues.
Just takes time and patience. Good Luck
US 1920 San Jose City Ward 4, Santa Clara, CA
self Vincent Guzzo M 33y Italy
wife Madelina Guzzo F 23y Italy
dau Antonia Guzzo F 7y Italy
dau Eda Guzzo F 5y California
son Joseph Guzzo M 4y California
US Census, 1940 Assembly District 25, San Francisco City, CA
head Vince Guzzo M 55 Italy
wife Madiline V Guzzo F 44 Italy
son-in-law Floyd V Mohr M 33 Arkansas
daughter Helen A Mohr F 27 Italy
granddaughter Lorraine M Mohr F 9 California
granddaughter Dolores L Mohr F 6 Californi