For what its worth, when I make a shadowbox, which is what this is, I generally make it so that it will NOT come apart. More than likely those items were meant to stay in place, which means they could be either hot glued or a strong enamel based cement. It's probably not worth it, there is no doubt if they have been sitting there for 25 years, they probably wont part in your favor. Just my experience and humble opinion. Good luck.