George Benson? I thought he was a jazz musician.
They didn't use epoxy, but polyester for your hull and deck, as with most boats even today.
The Contessa 26 is in my and many others opinion a better built boat. But its chainplates are bolted to knees that are heavily glassed to the hull, a very good solution if there are no bulkheads in the correct location. This could be done but will require good glasswork. Pic of Contessa chainplates below.
I doubt your cabin top is as thick as the hull.
If the chainplates are attached to a bulkhead, even one not glassed in, it still spreads the loads around a bit and the bulkhead is not likely to pull through the cabin top and deck. Especially as they were originally also bolted through the athwartships beam under the deck. Glassed bulkhead is of course better.
The hull type of attachment is in shear. The hull is also the strongest part of the boat. The cabintop for the most part is flat and there is not much to stop the plates from either pulling through, distorting the cabintop, or putting a lot of stress on the hull/deck joint.
How are you planning to attach the strut? And to which part of the boat as the liner isn't a good attachment point? The original chainplates in a Coronado are well attached for the type of sailing the boat is designed for. 2nd pic.