old (before 65?) vs new (65 and later) kickdown linkage question

I have been trying to help a member here with his small block kickdown linkages, which has led me to a question. On all the cars that I work on the kickdown is connected to the carb with a slotted adjustable rod. I believe that this is so that when you let off the gas quickly whatever is connected to the kickdown lever on the trans to come into place more slowly. At a recent car show I looked at a wide variety of Mopar kickdowns and those on late 50s/ early 60s cars seem to be connected rigidly to the carb stud - no slotted feature. Does anyone know why Chrysler changed this (what the actual function of the slot is)? Does it have to do with going from the push button trans to the newer ones?