Hello Ben,
first welcome to the forum!
The sheath isn't from Sumatra but from Bali/Lombok and called sesrengantan but not a very well carved one and I think that the blade is as well from Bali/Lombok not only because it is polished. Do you have opened the pendok which have a East Java/Madura style? Maybe it was attached because the gandar is damaged?
Regards,
Detlef