Make sure to leave out the DSDT/SSDT in /EFI/Clover/ACPI/Patched, not specific to your system. If you want them patch, hit F4 during boot in Clover, compress and attach /EFI/Clover/ACPI/Origin.
Boot with the USB installer, select the external drive to complete the installation.
Then install Clover to the external drive with same settings you use for the USB Installer. Replace /EFI/Clover folder with the one from your USB installer.
Reboot without the Installer.