I have a '47 Exhibit. There are two screws at the upper left and right of the head that hold a small piece of trim on. That lifts off, then the backglass can be removed vertically. Make sure that the insert board (the one that holds the lamps/transformer) is pulled back a hair (screws on the sides of the head), and use a small piece of painter's tape on the front of the glass to help you lift and pull towards yourself (the routed channel for the glass is larger than the depth of the glass).

Get your other hand underneath when you've lifted it enough and you can maintain even pressure forward and up all the way out. This should help you prevent scratches and other blemishes when you remove.

But you still have to be extremely careful. Unfortunately, modular backglass removal wasn't around for another couple of years (except in some Bally games).

Congrats on the Treasure Chest! I've had that one on my wishlist for a while now.