Use the latest EFI in post #1.
Change system definition to iMacPro1,1 in config.plist > SMBIOS.
Try adding "agdpmod=pikera" (without quotes) to config.plist > Boot > Arguments.
Install macOS.
If the screen goes black during installation, try unplugging and re-plugging the monitor cable. If that doesn't work, just leave it alone and let the installation complete. You can see if there's activity by watching the drive activity light on your case. To prevent sleep, randomly press the shift key on your keyboard.