Does it still have the stock undrilled throttle plates in it?
Is it a four corner idle unit or the front only type? If four corner adjust all of them, if not do what you can thumbs
If no extra holes in the throttle plates try the idle mixture screws and make sure the rear throttle shafts are not opened a bunch scope

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)