Seat frames and springs, are exactly the same as was mentioned. Cougars do have thicker foam padding than Mustang seat bottoms. Cougar floor seat risers are actually shorter than Mustang ones.
Seat bottoms are the same 1968-70 between Mustang and Cougar. You can just switch the seat backs from a 1969-70 to 1968's, if you wanted.
XR7 seat backs have storage pockets in them, they snap right on too.