Salaams all ~ Note for comparison. There are several sword groups that may have influenced the Kastane design and viable evidence suggests who may have delivered similar sword forms throughout the early years and encompassing(and bracketing) the first Portuguese arrival in 1505. I turn to "Islamic Arms" by the late Anthony North for two such swords for comparisons. The vehicle for such cross pollination in styles are possibly the famous sea traders of Sri Lanka; The Moors. (see note below*)
The weapon displaying quillons with remarkably similar dragon style finials from the above "Islamic Arms" is Quote"The hilt of carved jade mounted in gold, the blade of watered steel Persian, late 15th century Topkapi Palace, Istanbul".Unquote.
The weapons known as Nimcha are equally intriguing as to potential design influence where Moroccan style may have been transmitted.
Ibrahiim al Balooshi.
for a more detailed rendition of the Sri Lankan Moors..
Quote"Sri Lankan Moors (commonly referred to as Muslims) are the third largest ethnic group in Sri Lanka comprising 9.23% of the country's total population. They are predominantly followers of Islam. The Moors trace their ancestry to Arab traders (Moors) who settled in Sri Lanka some time between the 8th and 15th centuries."Unquote.