Try getting a putty knife or something else that is thin and rigid. Slip the knife between the trim and glass on the side that will lift. Gradually slide the knife toward the problem side while lifting the glass. This should guide the trim back into position and get it free. A second set of hands would probably help. I can send some pics of a bally backbox if you'd like. The top and bottom channels are individual pieces that are stapled to the body of the head. You could get a jimmy bar and pry one loose but your looking at repainting and repairing the damage.

If you have a set of these for setting the points on old engines/motorcycles I'll guaranty you can get a few blades in there. $4 at harbor freight or autozone. As far as removing the channel the easiest way is to score the top peice like in your first photo of the meteor and gently pry it out. It is stapled thru that piece, not the top of the head down. The bottom channel is groved to hold the base of the head and sides together with staples and wood glue. You would probably tear the whole thing apart trying to remove that end.

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I wouldn't try and remove the sides. The top has a tongue and groove that has been stapled and glued. If you remove the side you will most certainly break the joints and have to replace all 3 trim peices. This pic is from my fathom but I remember my lost world was built the same way.

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