The solution was to discard all the sage advice. I successfully created a bootable clone from the bootable thumb drive using an OWC Envoy Pro USB 3.1 Gen 2 SSD connected to a USB 3.0 port. It was slow, taking several hours for complete recovery, but it is bootable and 100% complete including a full restore from the Time Machine backup. How practical this would be to do very often is a subject of conjecture but more on that tomorrow. Right now it is past my bedtime.