The previous statement is true, C4 won't be any miracle for performance but it does require less power to spin. You will need a different driveshaft because the C4 is shorter than the AOD. Since the C4 hasn't been made for nearly 25 years or so you are looking at a rebuild as well. Also if you are searching for one be sure to look for one made after 1970 due to revisements such as input shaft, pump and valvebody. If you drive on the highway you might regret losing the overdrive.
Matt