The National Archives has copies of most naturalization papers, although it may depend on what court did the naturalization. If the naturalization took place in Pittsburgh, you will probably find copies at the Philadelphia regional office or at the main archives in Washington. There is also a book that has an index of most people who were naturalized in Allegheny County, indicating in which court or jurisdiction the naturalization took place. It is available at many libraries.

Note, though, that you're unlikely to find much more info than you found on the Declaration of Intent. Most of the naturalization papers give little more than the person's name, their sponsor, and their home country.