Hey Alex,
With regards to mounting the gate opener upside down, there's a fellow in Sweden who did just that, with the toothed rail mounted on the bottom of the rafters.
He has twenty or so videos on YouTube covering his entire build, from first dirt to completion.
https://www.youtube.com/playlist?lis...UQTFGzFSXjn9KQ
Hope this helps...
Cheers,
V