Thank you George, Tracy, and John.
George, I saw the AOP listing for the 60-pounder. Maryland Silver Co., the other outfit that sells plans, lists the Navy 100-pounder Parrott on a "broadside carriage," which is probably describing a Marsilly, because the only two carriages (as far as I know) that the US Navy mounted these guns on (aboard ships) were the Marsilly and the pivot carriage.
Tracy, I do have that photo of the "Powder Monkey" in front of the 100-pounder on the weather deck of the New Hampshire, and also the second period photo that you posted, in fact these are the only period photos that I've got (so far) that show the carriage. I compliment you on your exquisite taste, if for no other reason than that it agrees with mine;
seriously, I also think this photo is one of the best photos I've ever seen, bar none. You already mentioned a lot of its fine details, and in my opinion there's also the fact that this photographer had to be either a remarkable artist, or there was an incredible amount of serendipity that took place in achieving the near perfect composition of the picture. There are high resolution large giclee prints of this photo now offered for sale, and one of these days I'm going to get one.
John, Tracy has it covered, the USS New Hampshire was launched in April of 64, and it immediatley set sail to join the South Atlantic Blockading Squadron, it docked at Port Royal, South Carolina in July of the same year, and it served there as a store and depot ship until the end of the war. It's armament is recorded as consisting of four 100-pounder Navy Parrotts, and six IX-inch Dahlgrens. The CW period photo of the powderboy in front of the Parrott is shown on many different sites with captions that identify the ship as the New Hampshire, and the location as Charleston, SC.
So far I've got the two photos that Tracy posted, and three pics of a scale model; if anybody has anything more I'd appreciate it if you posted it here.
Model of a 100-pdr Navy Parrott, 26" long steel barrel, 1-inch bore.