Looking at forces going into bottom and top brackets from road bumps into the shock absorber cannot be much more than the spring fully coil bound plus the rubber bump stop on piston rod. So less than a ton my guess. That should be allright with the headlamp lugs of Bramptons - but then, it may look a bit more comfortable to use the mudguard lug below in the same alu bracket. That is my plan still, but certainly with modded Fournales oleopneumatics there, just 50 mm diameter and not even one kilogram/2 pounds.
Vic