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Can't you do it the other way? Put the temp HTML site on www - use the www2 to put the Drupal instance. Once the other is ready - remove the HTML & activate the Drupal version? Don't really understand what you're going to do with the www version while the www2 temp version is online. If not possible - can only agree with Egol - it's quite a risk you're running. Quite possible your rankings will take a dive. As we all know, it's easy to go down but a lot harder to regain position.