Looks like mostly complete Fold Down seat conversion on E-Bay.
http://www.ebay.com/itm/1971-73-Ford-Mustang-COMPLETE-folding-seat-/291025042982?pt=Motors_Car_Truck_Parts_Accessories&hash=item43c271be26&vxp=mtr#ht_563wt_1133
http://www.ebay.com/itm/1971-73-Ford-Mustang-COMPLETE-folding-seat-/291025042982?pt=Motors_Car_Truck_Parts_Accessories&hash=item43c271be26&vxp=mtr#ht_563wt_1133