I'm pretty positive that all Catalinas used either balsa or plywood coring in all of the decks, cabin top & cabin sides in order to give structural rigidity & save weight. I have removed ports in every Catalina that I've owned in order to rebed the port lights in our C22, C25 & C30. All similar in cosntruction, just heavier duty in the C 30. There is a 1/8" to 1/4" thick outer gellcoat & polyester fiberglass layer, inner balsa core at non- stress load areas such as the cabin house sides, (plywood used around higher stress loads at deck fittings) & an inner fiberglass liner sealing this sandwich. If the window frame is pushing out & deformed it is most likely core rot, where its loosing strength & deforming.
I doubt that its from compression post rot, as if it was that severe it would cause a very noticeable indention in the cabin top beneath the mast where compression fatigue would be seen. When you pull the aluminum port frame you can readily see the core material itself on the inner perimeter of the window opening. It was not sealed properly by Catalina, & any moisture that works its way in can cause the core material to delaminate & rot from within. If it looks really bad & your not willing to recore it then you're better off selling her to someone that is. Sometimes its a lot easier & less costly in the end to buy a boat in better condition then to restore a basket case. There's not such thing as a free or cheap sailboat. Good luck.
