It looks like yer gonna cast aluminum to the fork leg. If welded properly you shouldn't need the backer at all. both pieces beveled. Weld one side Back grind the other side and weld. A full Penetration weld. Tig or spoolgun. you should know what the fork is made of to know what filler to use If I remember right, the pads are stopped in the caliper and the caliper has a nylon button that keeps the caliper from spinning. I will look, my bike is in the garage.