First you need it to be on firmware 3.55 or lower. If it's not you will need a hardware flasher like e3 flasher or progskeet to downgrade it.
Second, you need at least the logic board from the blu ray drive working or you will not be able to run any homebrew.
At last, if it is on a higher firmware, you need to make sure the model is not too new. If it was on a firmware higher than 3.55 when it was from the factory, it will not be able to be downgraded.