Ok got the ARC installed.
Here is a test fit of the original length of the ARC:
Clearly too long, I couldn't even open the medicine cabinet in this configuration.
I hacked off 8" off one side to get a more satisfactory, er, arc:
A quick stop at Bed Bath & Beyond:
I ended up having to use the toggle bolts on either side (there was no stud in that spot). I did pick up some 1 1/2" 6-32 screws for the toggle bolts but they turned out to be too short: They didn't go far enough through the wall to allow the bolts to open up (really needed at least 2" screws). So I got out my dremel and trimmed down the 4" screws that came with the mounts to a length that would fit all the way through the wall but no further (measured using the mount and seeing how big of a gap was there between the mount & the wall when I hit the other side of the wall with the bolts).
When I was all done I grabbed a machine novel to the likes of Thor; it made this loud whirring sound and removed all the sawdust...was amazing! Thor should look into a machine like that!