\version "2.18.2"

voiceone = \relative c' {
    \set Staff.instrumentName = "Gtr3 "
}

voicetwo = \relative c' {
}

voicethree = \relative c {
}

voicefour = \relative c {
}

guitarthree = << \voiceone \\ \voicetwo \\ \voicethree \\ \voicefour >>