Running the ezflowupgrade.php script in the unzipped 4.3 package result is..
"Configuring...An unexpected error has occurred. Please contact the webmaster."
The fix is to edit /settings/site.ini and be sure the database settings are correct. In this case, there was no information filled in in at all.
Leading me to suspect the settings files were not copied earlier, missed a step. This was not the case.
In this version, the ezflowupgrade.php script is picking up database settings from /settings/site.ini when the use of that location is apparently deprecated in favor of more specific settings.
Regardless, to make it run, fill in the db information and the script will then make it past the "Configuring.. unexpected error"