Originally Posted by
Tim_Iowa
I wouldn't recommend you mount the light in that location, unless you use a front fender. I've heard of several failures of B&M lights when they got regular spray from below with water.
If you are planning on using a front fender, then I would reverse the mount to get the light as far back as possible, and bend the mount into a C shape make it fit. You can get longer mounts if that one doesn't have enough length.
A common light mount hack is to use an arm from an old centerpull brake to mount the light to one of the side supports. The SOMA wingmann mount is purpose-built but directly inspired by this hack.
Wingmann Light Mount | SOMA Fabrications
I will be using fenders, but they haven't arrived yet. Also this bike won't be seeing a whole lot of wet-weather use...I have another bike specifically set up for that. That said, a C-shaped bracket came to mind, although the one included with the light isn't long enough to bend into that shape.