It looks like the wording on the ZWO page may be a poor translation -- I'm pretty sure that they're talking about the Feathertouch focuser ONLY on the RASA scopes (since the adapter itself is specifically for Feathertouch focusers). So the assurance that it will work on the RASA 8 is only an assurance that it will work on the RASA 8 *with* a Feathertouch focuser installed. The page doesn't make that clear, but I'm pretty sure that's the case.
From your photo, I'm not sure how to rig this up. Making your own mounting adapter isn't very hard, but with the collar around the focuser shaft on the stock focuser, I'm not sure you can attach a coupler directly to it -- the collar gets in the way. The design of the collar on the Feathertouch focuser is different, which is why their mounting adapter can work with it.
Sorry I can't be of more help. You may be on your own on this one...!