Well, I just spent some time on the web trying to nail down the scale of the kit. What a confusing, frustrating experience.
The first link I got from Google was to Wikipedia. It contains a surprisingly lengthy article on the Harriet Lane: http://en.wikipedia.org/wiki/USS_Harriet_Lane
Most of the text apparently is based on an article in an historical journal by a gentleman named Tucker, with whom I'm not acquainted. There's some interesting information about the layout of the deckhouse (including, sure enough, the galley). But Mr. Tucker's article contains some alarming errors. Aside from the common mistake of labeling her "U.S.S.," he gives the wrong date for the ship's launch (she was launched in 1857, not 1859), and asserts that Harriet Lane was the niece of Senator (later President) Andrew Johnson - and that she served as "first lady" when Johnson became president after Lincoln's assassination. Miss Lane was in fact the niece of James Buchanan, who was president when the ship was launched; he was a bachelor, and brought Miss Lane to the White House to serve as mistress of social activities there. (A separate Wikipedia entry on the lady herself agrees with all that.)
More seriously, for modeling purposes, both Mr. Tucker's article and the Wikipedia entry give the ship a length of 270 feet. That's absurd. If the Harriet Lane had been 270 feet long (with or without bowsprit), she would have been one of the biggest wooden warships in history. Somebody obviously mixed up references to two ships. The modern medium-endurance Coast Guard cutter Harriet Lane, launched in 1984, is 270 feet long.
Having given up on that source, I tried the U.S. Coast Guard Historian's Office website. Its entry on the (original) Harriet Lane is relatively brief, but it should be reasonably reliable. Here's the link: http://www.uscg.mil/history/WEBCUTTERS/Harriet_Lane_1857.html
This source gives her a length of 180 feet - but doesn't specify whether that's the length on the keel, the length overall, or the length between perpendiculars, or the length on the maindeck, or what. I think somebody copied the number out of another source, without giving it much thought.
So, as a desperate last resort, I dug out the drawing of the Harriet Lane that I made for the CG Historian's Office back in 1989. (Gawd, I feel old - but that's not unusual these days.) I based that drawing on the one Merritt Edson made for the Smithsonian (the CG sent me a copy), and he worked from the original William Webb drawing. Unless either Merritt or I made an extremely stupid mistake (certainly possible in my case), the dimensions of that drawing ought to be right. It's on 1/96 (1/8" = 1') scale. It has an overall length (including the bowsprit) of 27 3/4". The length of the hull excluding the bowsprit is 24 1/8".
24 1/8" x 96 = 193 feet. I think that's the actual length of the Harriet Lane minus bowsprit.
That figure of 180', from the CG website, is believable if it's the length of the keel. (The length of the keel can't be measured from my drawing. It's the dimension from the extreme stern to the scarf joint between the keel and the stem, which doesn't show on an outboard profile.)
Several things are obvious from this exercise. One - the Coast Guard's records regarding its early history are a mess. (Anybody who's ever done any serious work on the subject knows that. The guys who work in the CG Historian's Office operate in a perpetual state of envy, thinking about their counterparts in the Navy.) Two - the description by Model Shipways/Model Expo of its kit as being on 1/96 scale, with an overall length of 18", is just plain wrong.
There's one good source to which I don't have convenient access: Donald Canney's book on early U.S. Revenue Cutters. Don is a good historian and an extremely conscientious researcher, and the book is quite recent. Unfortunately I don't have a copy. If I were doing really serious research on the Harriet Lane (or any other revenue cutter), that's the first place I'd look.
When I was much younger (much, much younger), I spent a lot of time poring over Model Shipways catalogs and dreaming about buying and building some of those kits. (The truth is that I probably could have built some of them to an acceptable standard - but, like so many young people who grew up in the age of the plastic model, I was intimidated by those wood and metal parts.) My recollection - which is extremely unreliable - is that the Harriet Lane kit was listed in the old, pre-Model Expo catalogs as being on the scale of 1/12" = 1' (i.e., 1/144). I remember being puzzled by what seemed a strange scale; none of the other MS kits were on it.
Doing the arithmetic, on the assumption that the MS kit has an overall length of 18", produces an overall length for the real ship (including bowsprit) of 216 feet. According to my drawing (on 1/96 scale), it ought to be 222 feet. That six-foot difference translates into half an inch on 1/144 scale. Pretty close; well within the tolerances that kit manufacturers typically observe.
Conclusion: the Model Shipways and Pyro kits are (or originally were intended to be) on 1/144 scale. I'll be more than happy to be corrected on the basis of further, reliable information, but I feel fairly safe in making that assertion.
One other little detail - the entry on the CG Historian's Office website includes a reproduction of that drawing showing the Confederates capturing the ship. (More precisely, it's an engraving based on that pencil drawing. I think somebody copied the caption, which includes the abbreviation "U.S.S.," from some other source that didn't know better.) It appears to show a simple molding inside the bulwarks. Whether the artist actually looked at the ship closely enough to be certain about such details I have no idea. I'm inclined to think he didn't; the deckhouse and several other features in the picture certainly don't match the plans. But that molding does look reasonable.