[luatex] accented characters in plain luatex

[Bob Tennent]

 >   Can you send the exact file you're compiling? 

A minimal example is

\input musixtex
\input musixsty
\title{Adagio}
\subtitle{(pour orgue)}
\headtitle{I. Adagio}
\shortauthor{D. Taupin}
\fullauthor{Daniel TAUPIN\\organiste à Gif-sur-Yvette}
\othermention{Composé en 1989}
\maketitle
\eject
\bye

where musixtex.tex and musixsty.tex are from musixtex-texmf.zip at

http://mirror.ctan.org/macros/musixtex/musixtex-texmf.zip