I included the pertinent MPC picture in reply #3. Since there was some confusion on the matter, it might help if we "read between the lines" as Jim refers to, right here and right now.
Focusing on the Mustang (F) and ignoring other car lines for years 67 through 70:
1967
There is a single entry for 67 (67 only, there is no "/" behind the number representing subsequent years). Both left and right are C60Z-3468-A. This strut rod is shared with 66/67 "B" (Fairlane)
1968
There is an entry for 68/69 (excepting Boss) with a RH part number of C8OZ-3468-A and a LH part number of C9ZZ-3468-D. Once again these are shared with the 68/69 "B" (Fairlane/Torino) cars.
1969
The 1969 non-Boss car is discussed above. There is another entry specifically for the Boss, with the RH part number of C9ZZ-3468-C and LH part number of C9ZZ-3468-D. It is interesting here to note that the LH part number for the Boss is the same one specified (in the 1975 version of the MPC) for the non-Boss 68/69 Mustangs. We would need to look at other data points (individual year MPCs, the OSI (Obsolete, Superceded, Interchange) books and so on) to figure out how this went down. I suspect that they had plenty of RH C8OZ-3468-A parts on hand but ran out of the LH C8 versions, and substituted those with the C9 variant for the standard (non-Boss) 69 cars.
1970
Actually the line item is for 70/ which would in the case of the 1965-1972 MPC that the parts are the same for 1970 through 1972. The parts are the same as the previous paragraph, with the RH part number of C9ZZ-3468-C and LH part number of C9ZZ-3468-D.
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A couple of general notes:
1. As has been stated multiple times, the MPC is a good reference in general, but not necessarily accurate for what was done at the factory.
2. The change from C8 to C9 parts, which the MPC associates with the "Boss", might apply to the Shelbys also. I don't see any "before/after" dates in the MPC, so I don't know if the different parts were in play on Job 1 or if they came later such as with the "big bearing" design. This is where input from experts on a site like this are very important.
3. I don't see why you would need to "settle" for a C8 part, especially since the C9 parts that the MPC calls out are used from at least 69 through 72. I did not check the 73 MPC, but suspect it would extend to that year also.
4. I have the 65-72 Mercury MPC but did not check it. I recall that the Cougar had a strange 2-piece job in 67.