Kitt:
Many of the reproductions are very close to the originals, including the cylinder engraving. However the "New York" barrel marking was used up to serial number 74,000 (and your gun is in this range) and then again as "New York U.S. America" between serial numbers 101,000 to 215348 (end of production).
If the revolver is an original one it should have a SMALL round trigger guard. Most, if not all of the reproductions have either a square-back trigger guard or a larger rounded one.
The original Colts had what is called "gain twist" rifling. The twist started out almost straight at the back and curved faster toward the front of the barrel. Modern reproductions have rifling that is a uniform twist throughout.
The letter "z" on the bottom of the barrel sounds more like a Colt inspector's mark then a European proof mark.
There is still much to doubt, but the revolver could be an original 3rd. issue 1851 Navy made before the Civil War.
