[Zeke]

The top rail of a DH vinyl window is not designed whatsoever for a cantilevered AC unit installation. However, I see some possible work arounds. The idea of wood or PVC struts under the top sash is a start. Adding a U-channel over the top rail will strengthen against bowing and breakage. You will also not be able to use the conventional bracing so plan on customizing some. You might consider moving the unit inwards a bit but not so much as to interfere with the condenser air flow. The units are initially designed to sit as far outwards as possible so that window treatments like blinds and curtains function.

This in a 2 man job in my book. And doable.