I think this is one case in which “follow the steps in reverse order” to reassemble is not quite enough when it comes to assembling the camera, earpiece, sensor, etc. I eventually worked it out and the repair was successful. This phone had been dropped in water and dried out by opening it and disconnecting the battery. Both the front camera and the ear speaker did not come back up and this repair/replace fixed it!
I bought the Pentalobe driver to use instead of the bit in the iFixit toolkit. It works a little better. I put in a new earpiece microphone in addition to the camera and sensor cable. Also, used the iFixit parts tray (very convenient). Total time for me was about 2 hours.
Thanks Sam, iFixit, and team!