R9 270X and R9 280X don't need anything to work in a Hackintosh, I have a MSI R9 270X and it works 100% OOB without any injection or selecting the framebuffer if I set InjectATI=True or select a framebuffer Futomaki it will go to black screen. Don't inject anything in the Graphics section. You don't even need the RadeonDeInit either, just make sure that the CSM is disabled in BIOS/UEFI.
I've been using HDMI and DP ports and both work ok.
You can use clover configurator to open the config.plist and under the graphic section there's a RadeonDeInit flag or open the config.plist and add the following code to under the Graphics section:
You might need to update your clover to the latest version because RadeonDeInit won't work in clover revisions prior to 4296 if I remember correctly.