Restoring MBP with macOS that is installed on an external hard drive
Carbon cloner did the trick perfectly.
It wiped the internal drive (I have a time-machine backup of the internal drive so I can get data if necessary), cloned the external drive to the internal drive. I then shut down the MBP, disconnected the external drive, and powered the MBP backup. It was identical to the external drive, so much so that I thought I double checked to make sure I hadn't unplugged the drive USB device.
Carbon Cloner has a trial version (5 free uses)! Nice!