Long time ago member and friend of Spirit, Dan Bunker had a beautiful red 88GT with a crate 4.9 installed. He did a glass insert in the decklid and had an image etched into it. I don't remember if it said Fiero or was the Pegasus logo. It did look really nice.
I recently read some discussion about doing the clear panel. There was discussion about material, whether a petrochemical product or glass was better. Seems that most thought the glass was the better for durability, but some voiced concerns with the ability to seal the panel to the deck lid due to vibration and different expansion rates of the decklid and material used for the panel.
I don't remember who, but I believe one person used a rubber gasket instead of bonding the panel to the deck lid. A see-through panel probably wouldn't weaken the lid any more than installing a scoop, though the scoop is usually bonded.