I ask because I bought a deck lid and spoiler at the salvage on Saturday. The car was an '88 but it was a base model, so I was surprised it had a wing on it. I didn't look at it closely until yesterday when I saw this:
Feel free to share photos of how your factory wings are mounted.
All Fiero spoilers carry the same overall design; a large main piece, with spoiler stands that carry studs with standard threads on one side and self-tapping style threads on the other. Simple nuts with built in washers secure the spoiler to the underside of the decklid. I off the top of my head don't know the thread pitch or size for the studs or the nuts.
The major difference is if the car is actually a notchback or a fastback. When the fastback was released in 1986, it carried a different underlying skeleton for the decklid "frame". The differences towards the rear made it that a notchback spoiler's rear studs would not properly protrude through the underside of the decklid. To remedy this, Pontiac simply moved the rear studs forward slightly. Very often individuals go out and buy salvaged spoilers thinking they're all the same and then run into this issue. It's not as prominent on a notchback than a fastback, since the notchback has less underlying support skeleton (in terms of the "meat" of the structure) than the fastback.
That looks correct. My 88 was built with the spoiler option. Buy the time I owned it many years later it was missing. The holes were there. I bought a spoiler from MooCow I think when he was going to school up here and installed it. I thought it was from a GT but I dont know for sure. Bolted right up.