Hi Ross,
Not sure if this is of any help to you in visualizing but worth a try (??). While replacing all our bulkheads below, we had to remove the chain plates which were covered by wood trim and then simply went straight up through narrow open slots to the deck and rigging. The attached photos shows the deck markings still on the old chain plates.
The plate holes below deck merely had bolts with heavy washers securing them to the original non-marine laminate bulkheads. (The second photo shows the plate back in place on the main bulkhead without the trim cover yet.)
My boat is of '73 vintage and I would suspect your design was fairly similar other than perhaps having a soft cabin top liner on your "C" model.
In replacing my bulk heads - I went with marine grade plywood and have sealed the edges and new holes with epoxy to insure any future water leaks don't permeate the wood.
We are also replacing our chain plates due to minuscule crazing and cracking by a couple of holes from a lightning strike many years back. We're having them made by Garhauer as he uses the water-jet method to cut the metal which doesn't heat the steel up to possibly weaken it.
Fair Winds - kerry