The NA engine is rated at 222 hp and the turbo engine is rated at 300-320 hp depending on the year.
The complete NA engine weighs about 300# and the complete Turbo engine weighs about 420#.
I think either engine would make a good swap in a Fiero. You would have a some challenges. You would either have to use the Mitsubishi transmission and get custom axles or get an adaptor plate and use the Fiero tranny. I don't know how everything would fit but people have put much larger engines into a Fiero and made them work. Also, I don't know where you would put the intercoolers for the Turbo engine if you choose that engine. Changing the intercooler to a Air/Water cooler would probably be the best bet.
As far as reliability, they are just like any other modern engine. The cars are all over 10 years old. They require maintenance and timing belt changes. They are likely over 100k miles so the valve stem seals probably need to be replaced. Head gasket problems are rare. The 6G72 engine uses a multi-layer steel (MLS) head gasket. These head gaskets are so tough that they are reusable. Expect to see burning oil issues that can be fixed by replacing the PCV valve and valve stems. Also be ready to replace the timing chain and water pump. Don't take the previous owner's word for it. Just replace them. If you take care of the engine, it is very reliable.
If you are looking for hp, then the Turbo engine can put out 400 hp in stock form with just some basic modification. There are lots of modifications that can be done that will get the engine into the 800+ hp range but you have to know what you are doing.
[This message has been edited by Doug85GT (edited 06-05-2010).]