Sweat of the brow is not currently and never has been a defense to copyright. Otherwise, copyright on books could be evaded by simply copying a book word for word.

The original composer owns the copyright on the arrangement itself. Your imperfect transcription is a separate derivative work but is still subject to the copyright of the original.

So the question remains: how do you plan on dealing with the copyright issues?

But if you can survive the copyright issues, the site itself is impressive.