Hi blanthauer, and welcome to the Forum,
The case hallmarks show that it was assayed in the London office in 1804, and the case maker was Matthew Need at 2 Castle Street, City Road, London.
I can't find a reference to an E Duncan, but this may well be a retailer. The movement has an unusual balance cock design, particularly the foot, and the steel plate, ("coqueret"), is also seldom seen on English movements. The dial numerals with minutes superimposed at the quarters is something I have not seen before.
Do you have any provenance for it?