Certainly a Madurese attribution would clear up some latent questions about this piece. The construction of the pendok in particular seems very "un-Balinese" to me and the form of the wranka is somewhat different from the usual Balinese godoan style cross-piece. The mendak also is certainly unusual, for Bali or Madura for that matter. It has the flavor of being only partial - perhaps part of a larger broken original.
A better sense of the scale of the piece would also be nice. No measurements? How have we come this far without measurements?
Speculation about the "originality" of the parts is at best, problematic, as we all know these things were changed on various whims at various times. That said, the gandar is very likely a replacement. Whether the repair was done in Indonesia or Europe will have much to do with what kind of wood was used. Indonesians usually use light weight, cheap wood for gandars when they are covered by a full pendok. I have a Yogyanese keris with a very similar gandar. Looks like balsa wood, though the rest of the keris is very fine quality indeed. And the workmanship is good. My guess - made in Indonesia.
I would hope that you will advocate strongly for the insertion of a new strip of black velvet or other, similar material behind the openwork of the pendok. Not exactly kosher for many conservation departments - or curators for that matter. I however always advocate restoration - as long as the methods and materials match traditional ones and the work is reversible. A good goldsmith will easily be able to match and replace the missing rivet holding the topengan to the top of the pendok.
As for the significance and mystical importance of the ganja iras - I'm afraid Nechesh, I cannot cite chapter and verse, and I'm too lazy to digging around to find it but I'd be shocked if no books mention it. Its one of those bits of knowledge one picks up on, talking to keris people around the archipelago. Certainly in Java, Sumatra and the Peninsula the ganja iras is, in my experience, usually spoken of in terms of its "speacialness" and this is usually connected to some magic property. If it were merely a matter of cheaper and easier, most keris would be ganja iras. Which is of course, precisely what has happened in the case of the Moro keris in the 20th century.
Now ganja hilang on the other hand - that's a completely different matter