In the current 3.07.0.1 plugin release, there isn't a proper version for the H16.5.
In any case, the plugin code has been updated and it is ready to work with the new Houdini 16.5 version. I'll include the first H16.5 plugin build in the next release, early next week, that is going to include also some of the new Octane 3.08 features.
This 3.08.0.0 build has a plugin version for Houdini 16.5. This is a test build, so it has not been added to the customer's download pages, you must download it from this forum topic.
The current 3.08 build has a proper plugin for Houdini 16.5. You can download it from the forum: viewtopic.php?f=102&t=64307
The 3.08 test plugin is only available for full commercial licenses. If you have a subscription license, please let me know to send you the links by pm.