I've owned my '67 Coupe for only 1 month. The car wouldn't hit passing gear, so I bought a new kick down cable. With the cable adjustment as short as it will go, it is still 1-2 inches too long.
I'm assuming that's the correct C4 transmission. I wouldn't think the throttle linkage has been replaced or modified. The cable I bought matched the one that was already on the car (come to find out, there was no need to buy a new one).
Did Ford make kick down cables of different lengths?
When I did mine (on a 68) the kick down lever on the trans was very short, so I set it at full travel with the accelerator at wide open throttle. When the accelerator was released there was about an inch or so of slack. IIRC.
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Well, most of the roof, rockers, and aprons are original. Getting closer...