I can't view the video here, so I can't see the car. 
But anyway...
Some problem areas:
-Aftermarket BS. (this goes for any car) look for out of place aftermarket garbage. If it has all sorts of nonsense bolted on there, it was most likely abused.
-Check the front spoiler area and make sure that everything is there. These cars are bottom-breathers, and I'm pretty sure there should be some ducting or an undertray that brings fresh air into the engine bay. If it's missing, there's a good chance it's overheated in the past.
-Check the cowl area for stress cracks, especially with T-Top models. This is common. they make chassis braces and stuff, but if it has a lot, I'd pass.
-On T-top cars, check out all the gaskets and T-bar for rust, and definitely check out the floor pans. If the T-tops leak, the floors get wet, and if the floors get wet, then, well, you'll probably need floors. 
-Check for oil smoke on start-up, especially on 305 cars. I remember a lot of those having bad valve seals after about 100,000 miles.
-Make sure all the important electronic stuff works, like the gauges, light motors, etc. Since it's a GTA, they are loaded with 80's electronic goodness. Some of it's bound to have failed by now.
-Also since it's a GTA, make sure the wheels are where they are supposed to be. They have different front and rear wheels with different offsets, and are labeled F and R on the inside.
I'm sure there's a lot more to look for, and you can always check out ThirdGen.org, which is a pretty decent forum/site for those. Good luck! 
