closed — a matter of forgetting to update the loose files in the wp root directory, and hence the wp-settings.php file where the includes are written.
We’ve decided to use a reverse proxy. There was an IIS plug in that did it nicely ( http://www.iis.net/download/applicationrequestrouting ) and then we didn’t have to migrate anything.
Thanks for your input!
** files permissions 644, directories 755
woops — you’re right.
I’ve changed those accordingly, but the problem persists.