Jeremy- as far as I can tell (from comparing the one's on my '94 Bravada) Tom is using "Blazer" style driving lights (which use an H3 bulb).
I'd be curious to see/hear about what fixture you're considering. I know that "Hybrid2M6" made his own (really cool) headlights, but it's a bit more involved of a project than installing something like Tom or Kris's system. http://www.fiero.nl/forum/Forum1/HTML/020580.html
Most people (all except one, KAZ, that I'm aware of) are using the vaccum-formed lexan headlight covers (about $60) from Kmunson56 - they are designed to be pressfit into the hood from below, and there is no additional mounting devices needed. The front of the lens has 2 tabs that fit into existing holes in the hood, and then the fixture itself bolts to the hood from below to hold it in as well. I don't see any way it could come loose.
Roger Garrison does also have lexan lenses on his Ferraro rebody- but they're simply held in place by velcro (and he's never had any trouble with them leaving the car).
soloyosh- I know what you mean about the protruding Corvette headlight assemblies... they're sweet (and run about $1k or more last time I checked). So, no... nobody's done anything quite like that before (although pisa had or has a hood that uses projector-style headlights in that kind of configuration). I don't know that there is anyone in the Fiero community looking to spend that kind of money on tooling for a product with such a small market.