how sure are you that your old boards were class legal? Could someone have modified the location of the through rope? My 5.2 boards had the same through rope but they still stuck up considerably at the top of the hull - you mentioned additional deck clutter with the new boards that leads me to believe your old boards go down considerably in the hulls?

I keep tearing the bumpers off of my 6.0 boards and I'm thinking about drilling them out and installing a piece of PVC tubing to put a through rope or a double sided solid "through" bumper in them.