I just got an 88 gta that came with a “classic industries’ 4th gen spoiler. It doesn’t have any hardware, and my hatch doesn’t have those little mounting tabs along the edge. How do I mount this thing? Is there a mount kit?

 

i drilled and screwed mine with i think it was 2 inch long bolts.
then i built the pedestals up with fiberglass and then smoothed and body worked them to look write.

I had that for a few years.

Then i bought a hawks reproduction wing and made it look factory again

 

Can you tell, or do you know if the hatch has been replaced? Kind of sounds like it might've been, because even if someone removed the original spoiler, there wouldn't have been much point in removing the mounting trim from the edges of the hatch.

The only one I see from Classic is this one that's actually reproduced and made for a 4thgen. Is this the one? I don't know what kind of hardware might've come with it, but it says mounting hardware included.
1998 Pontiac Firebird Parts | 10265846 | 1993-2002 Pontiac Trans Am; Fiberglass Rear Spoiler; One Piece Design; USA Made! | Classic Industries

Or do you have this one that Hawk's sells? It's a 4thgen-style spoiler that's actually made to fit a 3rdgen. This one, like the 3rdgen reproduction, should've come with mounting hardware for cars that didn't have an aero wing spoiler originally, or in your case, where the mounting trim has been removed.
82-92 Firebird Fourth Gen Style Fiberglass Spoiler - Hawks Third Generation

The main differences between the 4thgen-made-for-3rdgen and the actual 4thgen are the side "spears" (which should be more "pointed" on the one made for 3rdgen, versus "squared" or "chopped-looking" on the actual 4thgen spoiler), the brake light design, and the two inner supports. If you have the one I linked from Hawk's, then post some pictures of it please. The few pictures Hawk's shows, and the few that turn up in web searches, are distant and from poor angles, no side views, and no close ups that show any details and fitment. I've been wanting to see more pictures of it.

 

PO said it’s from classic but I think it was probably from hawks. It seemed to fit ok, think I can manage to bolt it down by the pedestals but trying to figure out what to do with the ‘arms’?

I think the hatch is it probably from a different car. I can see the outline where there would be 4 or so of those little spoiler mount brackets, but they’re all missing

 

A couple of pictures of the spoiler would probably confirm which one it is. Classic might've at one time sold the one Hawk's sells. It's been around for many years, and a couple of vendors have sold it in the past.

If the hatch looks like it had the mounting brackets on it, then it might be original. You said the car's an 88. An 88 will have a small white VIN sticker on the underside of the rear metal deck lid, which would confirm the VIN. If there's a sticker, it's probably right near the edge of the plastic interior trim piece, although you might have to remove the trim piece to see the sticker.

 

 

 

A lot of good pictures. That's what we needed to be able to see how that spoiler looks, instead of the few distant pictures that can be found online. Thanks.

Looks like the one made for 3rdgens. The "arms" or "spears," as they're sometimes called, are pointed like 3rdgen spoilers; actual 4thgen spoiler are "square." The two inner supports are made to reach the 3rdgen deck, unlike actual 4thgen spoilers that people have to modify to make them reach the deck on a 3rdgen. And the "missing" brake light is the type for the one made for 3rdgens. Kind of amateurish the way they carved the identification into the pocket for the brake light; maybe it was an early prototype. It should probably fit on the glass frame, not inside of the frame, because that's what it'll attach to, but that might just be the way you have it resting on the hatch, or maybe those arms will have to be pulled outward slightly to attach to the frame.

You could probably reach out to Hawk's to see if you can get some mounting hardware. Not sure where you'd get the brake light though, if you don't have it. Hawk's might be able to get one, but I kind of doubt they'd want to. Hardware might not be such a big deal to them, but a brake light probably would be.

What's the last picture showing? Is that showing how it hangs out over the decklid?