I think you first need to disconnect the kickdown linkage from the carb and see if you are getting full travel on the throttle cable. If you are using the two-barrel cable and bracket on your 4-barrel conversion, you probably aren't.

Have someone inside the car floor the accelerator and see if the carb is opening all the way. If it isn't, adjust the cable. If, after adjusting for full throttle the cable holds the carb partway open when the throttle is off, you need to modify the throttle cable bracket and/or change the cable itself. There should be no tension on the carb from the throttle cable at idle, and the carb should open all the way when the accelerator is floored.

Once you have that straightened out, THEN you can adjust the kickdown linkage. Same deal - the linkage shouldn't push the kickdown lever at idle, but should push it all the way back at full throttle.