With this code I pointed to the extension of a instrument (the horn). The code is correct, do you think? You can stop the diagonal line so that it does not overlay the treble clef?
\relative c'' {
\clef "bass"
\cadenzaOn
bes,,,1 \glissando \clef "treble" f''''
\cadenzaOff
\bar "||"
}
\layout {
\context {
\Staff \remove "Time_signature_engraver"
}
\context {
\Score
\remove "Bar_number_engraver"
\override SpacingSpanner #'uniform-stretching = ##t
}
}