One step forward!
I was successful booting to 10.14.5. Vega64 GPU is working. In MultiBeast, I ran into problems, and now I cannot reboot. I'm hoping I don't have to re-install. Here is what I did:
1. Changed BIOS as per JCMunsonII "BIOS Setup" (though I could not find XHCI Handoff).
2. Changed SMBIOS to "iMac18,3" and Binaries Patching to "0x05060E3"
3. Per JCMunsonII, jumped to Stork's Installation notes (Sierra Build) for MultiBeast tweaks.
4. In MultiBeast, selected:
- Quick Start > UEFI Boot Mode
- (I skipped the Audio drivers for now)
- Drivers > Misc > FakeSMC Plugins
- Drivers > Misc > FakeSMC HWMonitor
- Drivers > Network > Intel > IntelMausiEthernet
- Drivers > USB > USBInjectAll.kext
- Bootloaders > Clover v2.4K r 4063 UEFI Bood Mode + Emulated NVRAM
- (I skipped all graphics options. I'm using Vega64)
- I had in "Build", Customize > Sys Def > iMac > iMac 18,3
5. I saved this configuration.
6. I selected the drive "Mojave" (and not the opt. "Install Mojave" or something sim.), and I selected "Install"
It installed successfully.
I noticed, however, that neither the drive "Mojave" nor my system name were not present in Finder. It seemed that this would be needed to navigate to S/L/E and install "AppleHDA.kext" - per the JCMunsonII audio changes of "01/31/2018 - 02/01/2018 13.3 Supplemental Update..." So, I rebooted. My system would then crash each time I was 1/2 way through the Apple progress bar during bootup. I tried Verbose. From the Clover screen, I also tried booting from both the Mojave Installer (which prompted me to reinstall MacOS) and from by NVME drive "Mojave". Neither worked, despite making the above SMBIOS changes, etc).
At this point, I don't know what else to do. If I can boot again, I'd gladly use the Install_Tools reporting - if that would helpful to diagnose.
I am sure it is operator error, but I'm out of guesses and appreciate any guidance. Thank you!