You need to measure the travel of the carb throttle stud first. From closed to WOT. It’s likely to be about 1.150” +/- Regardless, At WOT you want the kickdown lever on the trans all the way back as well. I no longer run a kickdown (full manual) but when I did I had to drill a hole in the trans kd lever to get the ratio right. Also did this on a 78 Magnum (360/904) running a Street Demon 625 with the Lokar KD (original lever after being modified)