I managed to install it but first in an APFS clone as explained in my post. However it was a End 2013 MP and not your MP.Installed this on a 2009 Firmware updated MacPro 4,1=>5,1 and got stuck on boot for over 12 hours on 02/01/2019 finally rebooted and wouldn't start up. PRAM reset with removal of all non-system drives got me back in two weeks later got prompted to install it again. =(
Anyone else? Might skip this update since I pan to migrate to 10.15 in a couple of weeks.