Use calipers off a frog-eye Scorpio 24v. They are the same as cosworth 4x4 but use an M12 bolt instead of an M10, so they will fit the drilled out knuckles. File the edges of the caliper carriers so they fit the 283 mm 2wd cosworth discs and put a washer betweeen the caliper carrier and knuckle and it is all sorted.