Hello Jim! Thanks for coming in on this one. I see your point about the squared hilt being more toward the British pattern. I know this piece is a little rustic, but these private purchase types always attract my attention. Carribean...ahhh, now that would make me happy if it could be substantiated. I recall seeing a very primitive type sword similar to this listed as 'Cuban pirate', but that was in one of Fagan's catalogs, so...
Jim, you mention customs swords and police swords, which also had the ribbed iron grips such as boarding cutlass. I have a theory that these swords, which came after the said naval patterns, descended from them in an interesting way. In Annis 'Swords for Sea Service', there is an early cutlass with ribbed iron hilt and GR markings that was used by the West India dock authorities who guarded the ships and port. These authorities were both a division of maritime/naval power as well as the police/customs inspectors for the dock yards. I think it stands to reason that this is why we see the ribbed iron hilts on these type swords in the later 19th century. In any case, hope to research this sword a little more and await comments from others.