As I have just finished writing an essay on this topic, a lot of the information that will (hopefully) appear here will be similar to the essay. Why do to lots of research?!
In order to get a clear understanding of what a 'true Buddhist death ritual' is, you have to go through a lot of ethnographic accounts. After doing all this you will then realise that in actual fact there is no such thing as a 'true Buddhist death ritual'.
It works like this; most, if not all societies have their own traditions and practices. Within these are death rituals, and at the beginning they have nothing to do with Buddhism, it is only after Buddhism has been introduced and embraced by a culture does a Buddhist influenced death ritual appear.
When I did my research into the differences between the death rituals, I focused on three different places:
Each group had their own rituals and ideas, they also shared some common themes with each other.