My '83 has the same beam - 11.5 feet. I think what mainly changed over the years with the different models is the interior layout.
The first ones had the split bed in the aft cabin (along each hull). Plus the galley was on the port side in the salon with a dinette on the starboard side. The later ones had a double bed running along the starboard hull. Better arangement, but it took up half the lazerette. Plus they moved the galley to the starboard side, just to the right and behind the companion way ladder. The final models has a double bed running across the back (from port to starboard).
I would bet that the thru hull you have in the hall is the original thru hull for the engine intake. Somebody probably moved it if it is somewhere else.
I've never seen a diesel exhausted below the water line. Must be some reason for it. It would be a good idea if possible. Would make things quieter.
But there are reasons for not doing it -
- You could not verify that exhaust water is leaving the boat.
- Seeing the exhaust is a trouble indicator for the engine, dependent upon the color and amount.
Maybe you should make a post over on the gear maintenance board to get opinions from people that know more about engines. Guaranteed you will get 14 or 15 differing opinions..... :-)