Rick,
Yes, it seems to be. It is much more sophisticated than the usual Paiwanic blades. This one must be the result of a barter with a Chinese Han settler or a Japanese traveller. May be, it was also 'taken' away from someone outside of the tribe, at the same time with his head. We'll never know.
Kukulza,
The Paiwanic group is composed of three distinct groups: the Paiwan, the Puyuma and the Rukai. These 3 groups, despite some cultural similarities, are quite different. Languages are different, and even among the Rukai, it happens that in the same valley, 3 Rukai villages have 3 different dialects.
For what concerns the name, I checked my source, and as you wrote, 'tjakit' means a sword in the Paiwan language. The 'sisavavuavua tjakit' is the name for the common sword when the ceremonial sword is called 'sitjeqalaqala tjakit'.
In Rukai language, the Rukai sword should be called 'rinadrug'
Sorry I won't be able to tell you more
