Tony, haven't heard on several of your issues. Here is something on the after cockpit bulkhead.
On the 2nd page of this thread about half way down is one of Bill's photos from the first shoot that shows 338's cockpit with the aft 'bridge' cut away. It clearly shows the sides of the vertical hatch that provided access to the OB well and lazarette. The bulkhead is the ply that is closest to the inside of the lazarette. The ply that is closest to the cockpit is the filler.

The filler, in 338, is no wider or any longer than the well. The factory put it in to enable the drapping of the mat around the hatch there when they were closing the boat in. I suppose it could be a different shape in yours.

Is this the piece that came loose in 113? I really don't see any way the bulkhead could have moved even if there is lot of unsaturated garbaqe along the hull inside under the funky tabbing. The funky tabbing they never thought anybody would see - except you and me! The lazarette bulkhead is also tabbed to the hull on the laz. side. So it is very secure.

#6 photo shows the Bomar riser made from the mahogany strip liner in the hole with mishmash on the outside under the hatch bottom.

#9 shows the access under the chain locker, Just access. Three tubes: Straight one on left comes from drain hole in forepeak. Bent one on right sweeps up to hole in chain locker. Both will continue by conduit under the sole to the sump and end in threaded ball cocks. Short upright is a piece of the sonar model which is sculpted into the stem. Cheers................Ebb