There weren’t too many choices for an engine in a 1980 Trans Am.
If you really do have a truck engine in there it is most likely some form of a small block Chevy.
It’s not always easy to tell one small block from another so there really is no telling what you have but if you’re really wanting to swap it out anyway then it really doesn’t matter.
As has been said, the bell housing pattern is different on a Chevy engine when compared to a Pontiac (or Oldsmobile or Buick) engine so unless you plan on swapping both engine and transmission then you need to made sure at least what make of engine you have in the car.
If it’s a Chevy engine and you want to swap then probably the easiest way to go is with a 350. You have many options from building your own to buying a new crate engine.
Don’t neglect the transmission while you’re in there. Adding major horsepower to a weak transmission just means you get to crawl under the car some more later.
I used to have a Turbo Trans Am. While I agree with missileman that in stock form it was pretty weak, the engine really responded to an aftermarket cam and light porting/polishing of the heads.