Michael, could you post a photo looking down on the top of the sheath with the keris in it so we can better see the fit. From the photo you provided i would also venture that this sheath wasn't made for this blade. As for the blade origin, My first thought was also that it might be Javanese. Still, if i am not mistaken, you will find many Sumatran blades that look very similar to blades from Jawa as, i believe, parts of Sumatra where once under the influence of the Javanese court and therefore made their keris to Javanese specifications of the time.
BTW, the hilt is beautiful!
