Full width text and references in margin using marginnotes

Question

The tufte-book document class uses marginnotes to display references, and using the environment fullwidth allows sections of text to extend into the margin (the answer to my previous question gives an example of the latter). I'd use that document class were it not for the fact that using the packages amsmath and musixtex simultaneously results in an error - even the following produces errors when compiling:

\documentclass{tufte-book}

\usepackage{amsmath}
\usepackage{musixtex}
\begin{document}
Test
\end{document}

Note: I have all the prerequisite packages necessary for tufte-latex.

So I'd like to replicate those features without using tufte-book. Is this feasible, and if so, how would I go about doing it?

Answer 1

I stole some code from ceasar-book and fixed it for book.cls.

\documentclass{book}
\usepackage{chngpage}
\usepackage{amsmath}
\usepackage{musixtex}
\usepackage{showframe}

\newlength{\overhang}
\setlength{\overhang}{\marginparwidth}
\addtolength{\overhang}{\marginparsep}
%
\newenvironment{fullwidth}
  {\if@twoside\begin{adjustwidth*}{}{-\overhang}%
      \else\begin{adjustwidth}{}{-\overhang}%
      \fi
  }%
  {\if@twoside\end{adjustwidth*}%
     \else\end{adjustwidth}%
     \fi
  }

\begin{document}

\begin{fullwidth}
left \hfill right
\end{fullwidth}
\end{document}