FYI, my Pearson 36 has leaky chain plate covers and I knew I had to address that situation soon. As my electrician and I were rewiring the whole boat, we had the occasion to drill a one inch hole thru the "knee" that one of the chainplates was attached to. What we found was a piece of 1/4 inch plywood that was wrapped and tabbed to the hull with 1/4" of fiberglass on all sides.
I will dry out the knee, rebed the chain plate and bed the bolts that hold the chain plate to the knee. I think the plywood is to give the fiberglass a form, not so much for strength.
Attaching the chain plate to a bulkhead would seem to be OK as long as the bulkhead was tabbed, tabbed, tabbed...