General Lee,
I don't claim to be an expert, but everything I have on American uniforms at the time suggest that the Continentals' uniform coats were cut in a very similar manner to those of their English opponents and most regulars were so equipped towards the end of the war. That being said, it really depends on what specific unit you are doing for headgear and such, but a large amount of American equipment was from captured British stocks and the uniforms of Washington's units were often specified to be of British Regimental standards, often times in colors other than blue, and smallclothes (waistcoats, shirts, breeches, etc.) were pretty standard among all armies of the day with only minor differences. However, if I recall correctly American units fighting in the South were more ragged, as there was a higher concentration of militia, meaning there was rarely any regularity of uniform above company level.
So to answer your question, yes, the Perry plastics could work for Northern Continentals, but not really for Southern Contintals.
Again, I'm no expert, and will bow to the wisdom of those who are. For a good book covering the uniforms of the American Revolution I highly reccomend Don Troiani's Soldiers of the American Revolution.
Hope this helps!
-Chuck