This isn't for a mustang, but when I did the cable throttle for my '65 F100 I pulled the factory pedal assembly out of the truck. Heated up the top rod portion of the assembly with a torch and rotated it 90°, then used a die grinder to cut a notch in the top of it down to the hole that was originally used for the throttle linkage. For a cable I used one that was factory for a '77 t-bird (it was what I had.. and I was working with a 302 so it made sense). I drilled a hole for the cable to lock into, then bent the top of the rod again so that it could reach the cable end. In the top hole of the pedal assembly I did end up putting in a plastic spacer from the 'Help' section of the parts store. Since the motor was from the '77 t-bird it already had the bracket for the other end of the cable, but I did have to move the location of the mounting pin because the '65 F100 pedal did not have the same arc (movement length) as the t-bird..
It worked (and still works) great. No aftermarket parts were harmed during the making of this throttle cable setup. Maybe someday I'll have to try and remember to get some pictures.
-ron
