H28.5 Rigging
I, too, have an '86 H28.5 with no lines coming out of the double sheave box on the port side at the base of the mast. If you have wire ropes/lines coming out of yours, you may want to try tracing the other ends and that may give you a clue. If they go up the inside of the mast, they most likely come down the outside of the mast and terminate somewhere on deck. Lots of possibilities.