Hello Greg,
agree with everything what Alan, David and Jean have written so far. Two things are not mentioned until now, the first is that Ambon don't have an own keris culture, so Ambon keris isn't a correct description but it isn't unusual to find keris in other parts of Indonesia, I've found for example a keris blade on Halmahera!
Secondly, yes the hilt is from ivory but to my eyes it don't look like elephant ivory but it look like sperm whale ivory.
To remove the hilt heat the blade with a candle or carefully with a hot air gun and try carefully to move the hilt left and right, like said, very carefully that the hilt or pesi (tang) don't break.
Regards,
Detlef