A lot of the wartime production Colts look like they were hammered together using nail files and rusty forks to do the metal work. If authentic, this revolver has all the proper markings to have been made in 1864, including the inspector marks on the bottom of the barrel and on the trigger guard.
If this is a fake, someone spent a lot of time and effort to defarb an Italian gun, reshape the metal and grip frame to that of the wartime production fourth model (rather than the "third-ish-with-chunks-of-second-model-and-Brevete-bits" model that Pietta makes or the "mostly 3rd" model made by Uberti), and then took the time to defarb the barrel, buy the very expensive stamps for the mid 1860s Colt address "- ADDRESS COL. SAML. COLT NEW-YORK U.S.AMERICA - ", which has never been used on an import gun for legal reasons (as "America" on an Italian or Belgian gun is a violation of import laws), then, after taking the time to buy and use that very expensive stamp, they decided to cut half of the address off to make a snubby. They also took the time to put proper inspector marks on the barrel and trigger guard.
I've seen people do such crazy things, but they don't usually lose every screw and replace them with junk afterwards.
I have no clue where that wedge came from, but I'm leaning to "Period correct" on the rest. I can't say for sure without having it in my hand.
Please take the grips off and take photos of any markings on the inside of the grip channel. Also, please take pictures of the front and rear of the cylinder.
Thirdly, see if the rifling, if any, appears to be gain-twist. This might be hard since the barrel was shortened.
I am roughly 60% sure this is period correct but that other info would help a lot.