The steel cast caliper spacers and longer bolts used by the Porsche factory in the 914-6 GT rear calipers to allow a the use of a vented rotor is the very same hardware removed from a 1970/1971 Porsche 911 "M" caliper. In fact, the spacers from this pair of calipers were used as donor's to convert my 914-6 calipers to GT, and here is the finished product https://pbase.com/9146gt/factory_original_9146gt_parts_calipers_rear_set1_serrano Thanks Eric!

See photos below...