Note: I am not an engineer, but I have built a couple of bikes. Front end swaps, supermoto conversions, and a substantial application of baling wire and duct tape is fine but when braking is concerned, I often take the straight and narrow path.
A second look at your photos has me more convinced. If the lower mounting point has the bolt running through both brackets and the fork leg, it should take a good bit of the flexibility out of the system. As a precaution, I would get/make a sleeve for the upper bolt that with an ID that matches the bolt and an OD like that of the fork lug. This sleeve should then have enough clamping surface area between the brackets to reduce the amount of lateral force that the bolt is subjected to.
2004 YZ250F Dirt/Motard 1982 XLFTCR500 Street Tracker 1997 XR600R POS