Michael, thanks for showing this beautiful and unusal keris. I am really just guessing, but i am willing to go along with Lombok as an origin based more on the blade than anything else. It is my understanding that they went for more unusal daphurs in Lombok and this one certainly seems unusual to me. Hilts and sheaths can always be changed out so they are not the best proof of origin...and it would seem from the fit of the blade in the sarong that this is not an original marriage.
The naga seems very unusal to me as well because it has wings, and if i am not mistaken, a leg and paw along the bottom, so i guess it is actually meant as a composite animal (naga, garuda, singo???). Very interesting indeed. I can't really tell from these photos if this is orginal to the blade, but it seems possible that it is. Was there any provenence when you acquired it?