We spent 3 years on Nauru (no, not as illegal immigrants!) and during that time Air Nauru operated a 737 equipped as is this one here, for non-sealed strips.
Protruding forward of the engine intakes is bleed air to prevent stone ingestion, and fitted to the nose wheel a shield to prevent stones being thrown up.
It's a long time ago, but I think the only unsealed strip they used was Bonriki (Tarawa, ...TRW), in what was then called the Gilbert Islands & now Kiribati (pronounced "Kiribuss", the "-it" being sibillant).
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