OK guys, UPDATE. I got High Sierra to boot from Disk without UNIBEAST USB.
All I did was upgrade Clover to the one from MOJAVE Multi-Beast 11.3.0.
I believe it is now CLOVER v2.4k r4934
I had to add "-nv_disable=1" to the clover boot flags, for some reason it was/is missing.
So make sure you have a CARBONCOPY backup of your drive before doing this, just in case.
I discovered this while trying to upgrade from High Sierra to Mojave, following "upgrade directly to MacOS Mojave" instructions. That is not working yet. But getting closer I think.