The current Constellation in Baltimore is not the original frigate of 1797. It is the sloop-of-war that was the last sailing warship commissioned by the USN. The original frigate did have a flat transom, but was a smaller ship than the USS Constitution. Constellation was built as a 36 gun 18 lb frigate; Constitution was a 44 gun 24 lb frigate. I'm sure that with a great deal of surgery and a lot of research and scratch building that one could build a Constellation from the Revell Constitution but it would certainly be an involved project!
Unfortunately, I have never seen or heard of an accurate model kit of either of the Constellations. Artesania Latina produces a nice model of the current ship when she was incorrectly modified in the attempt to depict her as the original frigate. AL has not upgraded their kit since the ship was restored to her original sloop-of-war configuration in the late 1990s. I would love to see them do so, although I have seen some good conversions! The only other plastic model of the Constellation was a Pyro/Life-Like/Lindberg rendition of the museum's attempt to portray the ship as the original frigate. It is not really accurate for either the frigate or the sloop-of-war.
Bill Morrison