I agree with Ebb on that top bolthole:
The top holes on the upper and aft lower should not have been so close to the top of the plywood bulkheads. The bulkheads were in good shape generally, although I had to take off some water-damaged wood near that top boltholes and a few other places. I added #9 fiberglass cloth and epoxy to the bulkheads as needed and glassed the bulkheads to the overheads with epoxy. I then re-drilled the boltholes. The only place I did not have to add significant epoxy. Cloth was the forward knee.
Re-cutting the slots was a pain, but after the first three holes I got the hang of the process. Two small pilot holes, drilled one at a time near the sides of the former slot hole furthest from the bulkhead in question, followed by drilling two holes slightly smaller than 3/16. I think I used an 11/64 drill. Two jig saw (saber saw) cuts between the holes to create a thin rectangle slot. A thin flat fine file followed by a flat file just under 3/16 width. When the slots were completed and the chainplates dry fitted and temporarily bolted in place, I marked the precise size of the necessary final slots with tape if the slots seemed wider than I wanted. Two of my first three slots were a bit wide.
I then removed all of the plates, backfilled the slots up to the tape line with colloidal silica thickened epoxy where necessary, and check all slots for any voids, or stray pilot drill holes and filled these also. I used a putty knife. One of those West Systems epoxy resin/catalyst packages that come in the six packs was sufficient fort all of the slots. I did find one void a the top of the port forward lower just above the knee where my new slot nicked that void. My goal was to keep any water that might enter those slots from getting to any wood.
Tomorrow, I hope to bed the plates and bolt them securely in place. In the photo below of the port-side bulkhead that secures the rear lower shroud chainplate, you can see that the bulkhead has been epoxied to the underside of the deck. This should both make it stronger and also prevent any water leaking through the chainplate slots from getting to the top of the plywood bulkhead as was once the case.