Read final self comment below!
Work around for OWC SSD 10.13 GM Firmware Failure w/Mac Pro 2013
OWC 4TB SSD drives aren’t supported, swapped out for a smaller 1TB SSD drive and no issues with the upgrade...
Resolved the issue:
Removed: OWC 4TB SSD drive
Installed original SSD: Ran the 10.13 on this drive inorder for the Mac Pro firmware upgrade to succeed
Reinstalled the OWC 4TB SSD drive: Confirmed firware was present from previous GM install and then ran the install on the OWC drive without issue