Comparison of a Centaure Regular New Model Army and a Pietta 1860.
Differences right off the bat...
Grip shape, of course. The Centaure does not have the "Pietta tail"
Loading lever - The Centaure shows overlap between the two ends of the lever mechanism.
The gap at the front of the cylinder is larger on the Centaure.
The cut at the rear of the cylinder is larger on the Centaure.
The contour on the barrel, down around the wedge is different.
The Pietta is 4-screw, the Centaure is 3-screw.
That's quick and dirty without breaking out the calipers to measure stuff. You'll probably see other things. I'lll post the other sides, too.