Well, I got one of the single-bulb toyota light assemblies. In hindsight, I should've gotten a dual-bulb assembly, but I was going for dimensions. The following pics are provided as a comparison between the TFS and toyota light assemblies.
Assemblies side by side. You can see the difference in colors. The one on the left is the TFS assembly, and the lens is held on by glue, then screwed into place. The toyota unit has alignment tabs.

There are alignment tabs on the back of the toyota unit. The electrical connector does not come loose from the toyota unit. The toyota unit is about .25" wider, and thus would not fit without modifications.

You can see that the toyota lens is deeper than the TFS unit.

The units are almost identical heights.

The toyota unit has an angled lens.

The TFS unit has a flat lens.

The toyota unit is sealed, while the TFS unit takes a twist-to-lock light socket. The toyota unit is secured by a screw from behind.

My conclusion is that the toyota lenses are not compatible with a stock parking light assembly, due to the larger size, and the light socket/wiring differences. While the screw threads could be changed to machine screws for the Fiero, the mounts do not match up.
Edit: I'm not sure how the angled lens would work on a Fiero. I suspect that the light would be more down than forward, which would be good on an SUV, but bad on a low-slung vehicle like the Fiero.