Bill : Attached are copies from the 1967 Only MPC, showing the Rear Springs and the Bushings. Note that there is no reference to the Competition Suspension, or the Improved Handling Package. Also note that the Front Bushings for "Standard" Mustangs are shown as Part Number C4DZ-5781-C, as are they in the 1960-68 MPC. In looking at the 1965 Only and 1966 Only MPC's, they also show the C5ZZ-5781-A for the Mustang "Specials" only, and the standard Mustangs having C4DZ-5781-C.
Apparently, some time between 1968 and 1975 (when the 1965-72 MPC was printed), Ford decided to replace the C4DZ's with the C5ZZ bushings. Interestingly, this change does not appear in any of the OSI books between 1968 and 1981.
This supports what Bob G noted.
Also, instead of saying the Hi-Po bushings are the same as the Standard Bushings, it's actually that the Standard Bushing became the same as the Hi-Po bushings after sometime between 1968 and 1975.
Hope this helps.
Bob
P.S. I don't think that it is unusual that the "-AR" spring does not appear in the 1967 Only MPC, since the change noted in the 1960-68 MPC of 11/15/66, was probably too late to be printed in the January 1967 printing of the 1967 Only MPC.