Creating a "swing rhythm" indication

[Romel Bismonte]

Hello,

I was studying the LSR snippet that can insert an alternate rhythm indication 
(e.g., “swing”, “shuffle”, “maestoso”, etc.) as discussed in Item 204:

http://lsr.di.unimi.it/LSR/Item?id=204

Since I did not need the other options, I am attempting to boil down the 
snippet to just the thing I need. My attempt is as follows:

\version "2.18.2"

swingindic = \markup {
  \line \general-align #Y #DOWN {
    \score {
      \new Staff \with {
        fontSize = #-4
        \override StaffSymbol.staff-space = #(magstep -4)
        \override StaffSymbol.line-count = #0
        \override VerticalAxisGroup.Y-extent = #'(0 . 0)
      }
      {
        \relative c' { \stemUp b8[ b] }

        s4.^\markup { \halign #0 "=" }
        \relative c' { \stemUp \tuplet 3/2 { b'4 b8 } }
      }
      \layout {
        ragged-right = ##t
        indent = 0
        \context {
          \Staff
          \remove "Clef_engraver"
          \remove "Time_signature_engraver"
        }
      }
    }
  }
}

\swingindic

This works, but the first note cluster (the two eighth notes) are placed lower 
than the second note cluster (the triplet between the quarter and eighth note):

[cid:image003.png@01D59FF8.7E03ED30]

What can I do to align the note heads on the same line? Alternatively, what am 
I missing from the snippet implementation? At this point I am not opposed to 
using the whole snippet in my piece, but I ask here anyway as a learning 
opportunity to see how the markup works in this case. Thank you in advance for 
any assistance.

Romel Bismonte

P.S. I’ve been using Lilypond since Version 2.12, and I have to say it’s my 
most used program (together with Frescobaldi) as a choir director. Thank you 
for developing and helping to support such a great program.