Colin, a little reference material and similar items can be seen-
Boarders Away, by W Gilkerson, pg 89-90
Weapons of the American Revolution, by Warren Moore, pg 166
Swords/Blades of Amer Revolution, Neumann, plates 361S, 362S, 363S, 368S, 369S,370S,371S
It still could be Span colonial/Caribbean, as their patterns of West Indies cutlass very similar to Amer colonial and of the same time period.
Keep me in mind if you decide to part with it (

)...and Fernando, I saw it first!!