Thanks for posting the link, wanderer!
Comparing the Constitution Refit and the U.S.S. America will indeed require a very close eye for detail. As paraphrased from the book it came from, this class was the state-of-the-art, incorporating the latest tecnologies and adresed some of the perceived design flaws of its earlier incarnations. Many of the differences are very minor, like the wider support nacelles and repostioned dorsal thrusters, and some, like the rear firing torpedo and expanded impulse deck, are more obvious.
If someone were to tackle this particular Constitution, they really do have to be a stickler for accuracy.
I'm a little surprised it hasn't been done before, as it is the most advanced Constitution ever produced (according to Ships of the Star Fleet that is).