You can't directly swap a carburetor onto a throttle-body injected Fiero, and attempting to adapt a regular carburetor to the existing intake manifold would be a very difficult and likely unsuccessful project. The intake manifold itself is designed for either fuel injection or a specific carburetor, not both. Such a conversion would require extensive fabrication and custom parts.
If you have a carbureted Fiero, you might be able to replace the existing carburetor with a different one (of the correct type), but swapping to a throttle body setup from a carburetor would be a major undertaking. And vice versa (swapping from throttle body to carburetor) is equally impractical.
