The US 38 sculpt could be suitably generic to allow Constellation, Chesapeake and Congress and would satisfy the vast majority of wargamers I think. The differential in hull length between Congress and Chesapeake would be about 4mm and the overall appearance is pretty close, so a hybrid model pitched between the two in length would work.

How does the "SGN1xxA USS United States/USS Congress" idea work? Two ships in a pack? If so I'm not sure thats a good idea.