Also, you might be interested to know that I live in Italy and I see the name Svelto every day. It's a very popular dishwashing liquid sold everywhere and I prefer it over the other brands and have been using it for ten years. I don't know much about the origin of the product but you might want to do some research in this regard as Sveltos is very close to Svelto. The name Svelto will definitely ring a bell to consulate officials.
Eric. The original naturalization certificate will be fine but you may want to obtain the NARA documents as well. These can be certified by NARA, and you will find that they contain more information than the actual certificate. If you present an original certificate, they will return it to you and will keep a copy. You seem good to go.
I have the manifest of Pasquale Svelto. In it he lists his nearest living relative in Italy as his aunt with the same surname as his supposed mother (D'Avolio). It may not be slam dunk evidence but I would certainly assume it acts as supporting evidence along with other items.
Really, I'm interested to know what specific documents I may need IN ADDITION TO the typical documents in applying for Italian Citizenship with regard to a name change. I would assume since Pasquale Svelto is recognized as Italian, it's not his parents that are the issue but the name change. Are there any further documents beyond birth cert, manifest, naturalization (which shows name change), that I should look into?
Researching surnames: D'Errico, Bellotti (and other spellings), D'Avolio, Calvano, Marano
You need Pasquale's birth certificate from Italy which lists the name of his parents or some notes on the document explaining why the parents names are not there. You also need the birth certificate of the woman he says is his mother (the wife of D'Errico) and you need the marriage certificate of the D'Errico's.