Regarding the decorative work on the Hull model - another thing to remember is that, like most of the detail work on that model, it's pretty crudely executed. I confess that, when I had a chance to take a close look at it last summer, not having seen it for about twenty years, I was a bit surprised at how good the carvings are. And they're painted in bright colors that don't appear anywhere else on the model. (The transom window frames, for instance, are bright blue.) I wonder if the basic hull and deck details, on the one hand, and the carved ornamentation, on the other, were done by different people.
Several modelers have commented on the fact that the ship's name isn't carved on the stern of the Hull model. To my mind there's a simple explanation for that: the task of carving or painting such small lettering was simply beyond the task of the modeler. (He wasn't up to the task of making a steering wheel, either.) The words "Model of the U.S. Frigate Constitution. Presented by Commodore Hull." are painted neatly on the starboard side of the hull; that lettering, though, pretty clearly was added some time after the model was built.
Incidentally - I just took a look at some of the photos of the Hull model that I took last summer. It does have a pair of horizontal boat davits sticking out of the upper transom - but no davits on the sides.
The recent book Anatomy of the Ship: The 44-Gun Frigate U.S.S. Constitution, by Karl Heinz Marquardt, contains some serious inaccuracies (which we've dissected pretty thoroughly elsewhere in the Forum). One if its best features, though, is a set of reconstructed drawings (on p. 67) of four configurations of the transom. In this case Mr. Marquardt tells us the sources on which he based the drawings: the Corne painting of 1803 (eight transom windows), two Corne paintings from 1812 (five and six windows, respectively), and the current configuration (three windows). Mr. Marquardt's apparent failure to examine the Hull model is unexplained - and hard to excuse. But he obviously did take a good look at the contemporary evidence regarding this particular part of the ship. George Campbell, when he was working on the plans for the Smithsonian model (and, though he presumably didn't know it at the time, the Revell kit), did look at the Hull model. The carvings on the Revell kit look to me like a thoroughly reasonable interpretation of those on the Hull model - i.e., what the carvings on the real ship, which got translated into the slightly primitive renditions on the model, looked like. There's certainly plenty of room for interpretation about all this (as there is regarding so many other details of this great ship), but until I see some hard evidence to the contrary I'm inclined to think Revell's rendition of the bow and stern carvings is as believable as any.
Regarding the United States's "roundhouse" - I don't think anything can be said for absolute certain. Howard I. Chapelle, in the plans he drew for his History of the American Sailing Navy (1949), included a generalized reconstruction of it that certainly looks reasonable to my eye. I can recall seeing at least one photo of the ship, obviously taken late in her career; unfortunately the after part of the hull was blocked out by another ship, so that was no help. And to my knowledge the "roundhouse" doesn't show in any of the contemporary paintings or engravings of her.
One point regarding the armament, or lack thereof, on top of the roundhouse (and, for that matter, the poop of H.M.S. Victory): guns were enormously heavy things, and the beams and other structural members of a deck high up in the superstructure of a ship were relatively light. I suspect that, in both of these cases, the people responsible figured that putting such weight so high up in the ship would be dangerous.
One source that doesn't get consulted often regarding the Victory is a series of watercolor sketches that the great artist J.M.W. Turner made on board her shortly after she got back to England after Trafalgar. (Turner eventually made two major oil paintings that feature her.) One of those sketches (reproduced in H.M.S. Victory: Construction, Career and Restoration, by Alan McGowen and John McKay - though I may have garbled the title) shows the break of the poop. It doesn't look much like the ship does today (though it closely matches an 1803 model at the National Maritime Museum). It does show a rather large swivel gun mounted on the stanchion at each end of the poop rail. To my eye, at least, swivel guns mounted on the railing surrounding the United States's roundhouse would look pretty reasonable.