Re: 1974 Glastron
Be extremely careful until you pull the deck, I might not use it until that had been resolved. My 1960 Glastron FireFlite had no flotation foam below deck & my stringer system was wood-free so I didn't have any additional wood to remove after getting the deck up. Lots of work since, but at least I didn't need to replace the stringers or remove waterlogged foam.
By 1974, Glastron may have changed the way they built boats. Your transom is also wood encased in fiberglass and succeptible to water intrusion, ESP if near a soft deck.