i don't know the dimensions of the mount, but it looks like it's a little larger than the cf100 mount, maybe by a few mm in each direction.
i wouldn't be surprised if you can use a 128 in it. i currently have an old transcend 32gb class 10 card in it that was used in one of my smartphones for a year or so. i may later put one of my samsung evo 64gb class10 cards in it, once i get the action camera footage off it.
sorry i meant the dimensions of the camera not the mount. what's the horizontal distance on it? trying to see if it fits behind my mirror