[Jim McDougall]

I agree with Mark, totally fascinating entry on the Sumatran possibility, and the similarity is compelling. What I found most fascinating in the sword of the OP is that curious octagonal escutcheon on the guard. As you note, the tradition of the lionhead seems to have well influenced numbers of hilts throughout the VOC spheres in the East Indies.

While the 'sinha' (=lionhead) of the kastane appears to have either derived from the European lionheads so often on Dutch swords, or evolved indigenously from earlier symbolism of the lion, the parallels are compelling. Whatever the case, the stirrup hilt with lion head hilt in the character of the religious symbolism of these regions is well known as European influence affected the court and status oriented swords of these regions. As noted in the excellent entry in Peter's site on the pedang lurus, these seem to have been nominally influenced by European hunting swords, and the gestalt is remarkably notable.

With the octagonal escutcheon on the guard of this sword, I am inclined to think perhaps it is intended to represent the Ka'bah, which among other things is regarded as the Qu'ranic symbol of paradise. As Sumatra is predominantly Muslim, perhaps this might be the intended representation.

The Ka'bah is apparently often used in Islamic architecture, and of course various material culture. It seems in many elements of arms decoration, architectural features serve as inspiration for their design.

As noted in earlier discussion, this escutcheon does not seem particularly ergonomically friendly, but then neither is the hilt of the kastane. These are intended as court or dress type accoutrements and not as primarily combat weapons.

As far as I have seen, the octagonal escutcheon on this example is the only one I have seen on sword hilts, and it would be interesting to see the use of this symbol on other hilts or decoration.