Are you required a seperate handbrake in Switzerland? All rally cars I've dealt with use the hydraulic handbrake inline with the standard 4 pot rear calipers and no seperate handbrake caliper.
Demon Tweeks sells a direct bolt in dual master cylinder setup that can allow adjustment of front to rear bias also.
On the Group A pre-pneumatic center diff cars,Ford's hydraulic handbrake had dual master cylinders, one of which was a clutch master cylinder that disengaged the clutch disc as well to keep from ruining the center diff when you lock up the rear wheels but still have power to transmission. You could try to find that part or fabricate it pretty easily.