On USA parts made USFA's the cylinder flutes are not as pointed as on Italian parts guns, the ejector shroud housing cam is longer on USA parts guns, the firing pin is cone shaped on USA parts guns, the front sight is the same thickness from top to bottom on USA parts guns (Government Series guns are the exception), when the loading gate is opened the little hole where the loading gate pivot post goes into the frame is a small triangle and not rectangular or square, and the loading gate pivot arm is thicker on USA parts guns. As I stated earlier good photos of those areas would help. There may be other things one could identify that would help but at the present I cannot think of them.
I do remember one other, the checkering on the hammer spur is cut and not cast I believe.
I am certainly no expert but those are the things I have learned to look for in an attempt to identify USA parts guns from Italian parts guns. Others here probably know other ways to identify them. Somewhere Yahoody posted a article with photos on some of the things I have mentioned but I have been unable to find it. Up in the thumbtack area of this forum is a post by Yahoody about the little hole that shows where the loading gate pivot post fits into the frame.