That's Pietta's version. While a nice gun it is not really a true repro of the N.Y. Metro pistol. It's basically a short barrel 1861 Navy with partial flutes cut on the cylinder.
The original was built on the smaller .31 sized frame, with a rebate watertable and cylinder to handle .36 caliber, and it was a 5-shooter..
Uberti makes a more accurate repro.
I don't know what modification you're talking about.
I learned a few things about the Pocket Police by reading this thread. --->>> https://www.thehighroad.org/index.php?threads/who-loves-the-1862-pocket-police.347292/
It appears that there's a modification that was recommended by mec, a THR member who wrote an informative book about many C&B models.
I have a Pietta on order, the cap cut out is larger and a bigger trough than my Uberti one. I think both are same 31 frame tho. The Pietta I intend to shoot alot. My Uberti works OK the few times I shot it, but it is too pretty to shoot regularly.