The hilt is old, although not the oldest style I think we can identify. I think it has been with the blade since it was first mounted.
It is very hard to put a date to the hilt styles other than old, older, oldest type classification.
You have what I tend to think of as the second oldest style. The pommel is large but more of a lozenge shape than rounded. A medial ridge is defined. The guard is not boxy, but rather a wing shape, swelling where it meets the grip. The grip tube is round, not multi faceted.
Zacona I think will refer to the town, the phrase would be odd in Serbian or Croatian and in any case would require a K not a C. The blade is of a type that was widely exported including the well known firangi swords of India.I own one similar, see attached. I think the blade can be older than the 18th century, but I am not the best for dating this blade style. Better images will help when it arrives.
I am including images of what I would consider to be older hilt styles as well, hopefully what I am describing is visible from these images. In any case I think the blade and hilt are an authentic and original marriage and the sword is an excellent example of a hilt that has been with the blade for a very long time.