I have never owned a 66-69 Fairlane /Torino/Cobra with a small block or C4, but my understanding is that there is a difference in the height of the trans mount between a 289/302, and the FE transmission crossmember. No idea how much of a difference, though, as all my 66-69 Fairlanes/Cobras have been 390 (66) or 428 (69s), with C6s or a Toploader 4 speed.