I have an 83 5.8. It was the "standard" but as soon as the NA became available I upgraded to improve downwind performance. It helped but there are also other advantages to the NA kit. With the bridle foil you eliminate a lot inward pulling forces on the bows caused by a regular bridle. The NA kit also includes beam inserts to strengthen the main beam near the hulls. I later added a spinnaker to improve downwind performance even more.
Buzz