So, found some options to add American unrateds--these are my preliminary thoughts for two composite sculpts.

Brigs:~240-300t Argus/Syren/?Rattlesnake (all three UK reflag), Spark (similar size) - two SKU's for the American ships, one UK reflags
Chippewa/Boxer/Saranac are similar to one another but 360-390t; not appreciably larger in length/beam than the smaller trio
Schooners: Enterprise, Experiment, Syren, Nautilus, Torch (similar but not identical), Spitfire (ditto) -- Enterprise/Syren/Nautilus rerigged as brigs, Syren and Nautilus captured by UK (Siren not commissioned, Nautilus->HMS Emulous)

This group of schooners has several possible packs--three US flag schooner-rig and one brig-rig, leaving loose ends of the third rerig and Emulous.