I see where the 1975 dated MPC lists C9ZZ parts for fixed seat, and D0ZZ parts for fold down seat, and I acknowledge reading Ed's note on the difference in the curve.
I picked up a handful of these the other day from someone that has been fixing Mustangs for 50 years. Fixing, not restoring.
Referring to the attached document, when comparing the C9 and D0 parts, the curve is identical. I can't see any difference. However, just because these have C9 and D0 molded into the part does not mean that they were C9ZZ and D0ZZ service parts. These were almost certainly take-off original parts.
The question that I have is on the part identified as SPEC? There are a few differences compared to the others, the most notable is that they are "taller" and "shorter", noting the dimensions included.
Has anyone seen this? I have 9 non-SPEC and only 1 marked as SPEC. Thanks in advance.