swing eighths in tempo marking

[Donald J. Stewart]

I'd like to set something similar to 'eighth note = triplet' (attached tempo marking)

I see 'Beat Change' under Directives -> Markings -> Tempi and Metronome marks

But for some reason I get an 'unable to typeset' warning when I attempt to use this.

I'm sure there's a simple solution that I'm just overlooking...

(I also inadvertently sent this message to the lilypond-usr group -- of which I'm not a subscriber, evidently)

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