As a nation state, Italy has emerged only in 1871. Until then the country was politically divided into a large number of independant cities, provinces and islands. The currently available evidences point out to a dominant Etruscan, Greek and Roman cultural influence on today's Italians.
Your question involves statistics but what you want to know can best be described as "hearsay" There is a website that has more exact data on the subject. In answer to your question First cousin marriages in Italy in the late 1800's were few and far between and represented less than 1% of Marriages in a synopsis of the website www.gutenberg.org/files/29955-h/29955-h.htm
The Italian parish records usually say that special permission was obtained. Often because the bride was pregnant. I researched a case where an uncle married his niece and special permission was requested from the Vatican.
Remember that during the 1800's in Italy, the marriage was arranged by the parents, so boys and girls had not the chance to chose someone to marry, like nowadays.
At that time, parents arranged the marriage, and before the marriage the couple used to go to notary to write down a record stating what is brought in this new born family (properties, lands, houses, furniture, pots, dishes, beds, pillows, chairs, sheets and so forth)
So it was arranged by the parents, so the parents knew that the couple somehow had a solid future.
I hope it helps
I've seen numerous cases of 1st cousins (or closer!) marrying in the project I'm working on of mapping out an entire Sicilian town's family tree (pop 5000+) in the 19th c. but I haven't attempted to compile statistics on the phenomenon yet. It was not rare. I've never seen any kind of notation on any marriage cert either to indicate that special permission was required, even when a man married his niece.
I saw one family recently in which a man married his brother's daughter in 1930, a different man married his sister's daughter in 1923, and the children of these 2 unions, who were themselves 1st/2nd cousins (1st cousins from his perspective, 2nd from hers), then wed. I was researching the genealogy of the granddaughter of these 2 people - I hope she wasn't too shocked.
I wonder if such intermarriage was more common in that province or town. Was Ribera a trailer park?
Someone from a well-to-do family in a neighboring town told me that intermarriage used to be common among the aristocracy to keep the wealth within the family, but I've seen it as much or more among peasants.
I have 2 mothers in my tree who's children married each other. The children could be first cousins, I haven't been able to find who either of their mothers parents are. I've heard it was common, especially in Lipari. Small island and I guess slim pickings and all that.